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<li class="md-nav__item">
<a href="#1" class="md-nav__link">
1. &nbsp; 基于分治实现二分
1. &nbsp; 基于分治实现二分查找
</a>
</li>
@@ -3307,7 +3307,7 @@
<li class="md-nav__item">
<a href="#1" class="md-nav__link">
1. &nbsp; 基于分治实现二分
1. &nbsp; 基于分治实现二分查找
</a>
</li>
@@ -3371,38 +3371,38 @@
<p>我们已经学过,搜索算法分为两大类。</p>
<ul>
<li><strong>暴力搜索</strong>:它通过遍历数据结构实现,时间复杂度为 <span class="arithmatex">\(O(n)\)</span></li>
<li><strong>自适应搜索</strong>:它利用特有的数据组织形式或先验信息,可达到 <span class="arithmatex">\(O(\log n)\)</span> 甚至 <span class="arithmatex">\(O(1)\)</span> 的时间复杂度</li>
<li><strong>自适应搜索</strong>:它利用特有的数据组织形式或先验信息,时间复杂度可达到 <span class="arithmatex">\(O(\log n)\)</span> 甚至 <span class="arithmatex">\(O(1)\)</span></li>
</ul>
<p>实际上,<strong>时间复杂度为 <span class="arithmatex">\(O(\log n)\)</span> 的搜索算法通常是基于分治策略实现的</strong>,例如二分查找和树。</p>
<p>实际上,<strong>时间复杂度为 <span class="arithmatex">\(O(\log n)\)</span> 的搜索算法通常是基于分治策略实现的</strong>,例如二分查找和树。</p>
<ul>
<li>二分查找的每一步都将问题(在数组中搜索目标元素)分解为一个小问题(在数组的一半中搜索目标元素),这个过程一直持续到数组为空或找到目标元素为止。</li>
<li>树是分治关系的代表,在二叉搜索树、AVL 树、堆等数据结构中,各种操作的时间复杂度皆为 <span class="arithmatex">\(O(\log n)\)</span></li>
<li>树是分治思想的代表,在二叉搜索树、AVL 树、堆等数据结构中,各种操作的时间复杂度皆为 <span class="arithmatex">\(O(\log n)\)</span></li>
</ul>
<p>二分查找的分治策略如下所示。</p>
<ul>
<li><strong>问题可以分解</strong>:二分查找递归地将原问题(在数组中进行查找)分解为子问题(在数组的一半中进行查找),这是通过比较中间元素和目标元素来实现的。</li>
<li><strong>子问题是独立的</strong>:在二分查找中,每轮只处理一个子问题,它不受另外子问题的影响。</li>
<li><strong>问题可以分解</strong>:二分查找递归地将原问题(在数组中进行查找)分解为子问题(在数组的一半中进行查找),这是通过比较中间元素和目标元素来实现的。</li>
<li><strong>子问题是独立的</strong>:在二分查找中,每轮只处理一个子问题,它不受其他子问题的影响。</li>
<li><strong>子问题的解无须合并</strong>:二分查找旨在查找一个特定元素,因此不需要将子问题的解进行合并。当子问题得到解决时,原问题也会同时得到解决。</li>
</ul>
<p>分治能够提升搜索效率,本质上是因为暴力搜索每轮只能排除一个选项,<strong>而分治搜索每轮可以排除一半选项</strong></p>
<h3 id="1">1. &nbsp; 基于分治实现二分<a class="headerlink" href="#1" title="Permanent link">&para;</a></h3>
<h3 id="1">1. &nbsp; 基于分治实现二分查找<a class="headerlink" href="#1" title="Permanent link">&para;</a></h3>
<p>在之前的章节中,二分查找是基于递推(迭代)实现的。现在我们基于分治(递归)来实现它。</p>
<div class="admonition question">
<p class="admonition-title">Question</p>
<p>给定一个长度为 <span class="arithmatex">\(n\)</span> 的有序数组 <code>nums</code> 数组中所有元素都是唯一的,请查找元素 <code>target</code></p>
<p>给定一个长度为 <span class="arithmatex">\(n\)</span> 的有序数组 <code>nums</code> 中所有元素都是唯一的,请查找元素 <code>target</code></p>
</div>
<p>从分治角度,我们将搜索区间 <span class="arithmatex">\([i, j]\)</span> 对应的子问题记为 <span class="arithmatex">\(f(i, j)\)</span></p>
<p>原问题 <span class="arithmatex">\(f(0, n-1)\)</span> 为起始点,通过以下步骤进行二分查找。</p>
<p>原问题 <span class="arithmatex">\(f(0, n-1)\)</span> 为起始点,通过以下步骤进行二分查找。</p>
<ol>
<li>计算搜索区间 <span class="arithmatex">\([i, j]\)</span> 的中点 <span class="arithmatex">\(m\)</span> ,根据它排除一半搜索区间。</li>
<li>递归求解规模减小一半的子问题,可能为 <span class="arithmatex">\(f(i, m-1)\)</span><span class="arithmatex">\(f(m+1, j)\)</span></li>
<li>循环第 <code>1.</code> <code>2.</code> 步,直至找到 <code>target</code> 或区间为空时返回。</li>
<li>循环第 <code>1.</code> 步和第 <code>2.</code> 步,直至找到 <code>target</code> 或区间为空时返回。</li>
</ol>
<p>图 12-4 展示了在数组中二分查找元素 <span class="arithmatex">\(6\)</span> 的分治过程。</p>
<p><a class="glightbox" href="../binary_search_recur.assets/binary_search_recur.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="二分查找的分治过程" class="animation-figure" src="../binary_search_recur.assets/binary_search_recur.png" /></a></p>
<p align="center"> 图 12-4 &nbsp; 二分查找的分治过程 </p>
<p>在实现代码中,我们声明一个递归函数 <code>dfs()</code> 来求解问题 <span class="arithmatex">\(f(i, j)\)</span> </p>
<p>在实现代码中,我们声明一个递归函数 <code>dfs()</code> 来求解问题 <span class="arithmatex">\(f(i, j)\)</span> </p>
<div class="tabbed-set tabbed-alternate" data-tabs="1:12"><input checked="checked" id="__tabbed_1_1" name="__tabbed_1" type="radio" /><input id="__tabbed_1_2" name="__tabbed_1" type="radio" /><input id="__tabbed_1_3" name="__tabbed_1" type="radio" /><input id="__tabbed_1_4" name="__tabbed_1" type="radio" /><input id="__tabbed_1_5" name="__tabbed_1" type="radio" /><input id="__tabbed_1_6" name="__tabbed_1" type="radio" /><input id="__tabbed_1_7" name="__tabbed_1" type="radio" /><input id="__tabbed_1_8" name="__tabbed_1" type="radio" /><input id="__tabbed_1_9" name="__tabbed_1" type="radio" /><input id="__tabbed_1_10" name="__tabbed_1" type="radio" /><input id="__tabbed_1_11" name="__tabbed_1" type="radio" /><input id="__tabbed_1_12" name="__tabbed_1" type="radio" /><div class="tabbed-labels"><label for="__tabbed_1_1">Python</label><label for="__tabbed_1_2">C++</label><label for="__tabbed_1_3">Java</label><label for="__tabbed_1_4">C#</label><label for="__tabbed_1_5">Go</label><label for="__tabbed_1_6">Swift</label><label for="__tabbed_1_7">JS</label><label for="__tabbed_1_8">TS</label><label for="__tabbed_1_9">Dart</label><label for="__tabbed_1_10">Rust</label><label for="__tabbed_1_11">C</label><label for="__tabbed_1_12">Zig</label></div>
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<h1 id="123">12.3 &nbsp; 构建二叉树问题<a class="headerlink" href="#123" title="Permanent link">&para;</a></h1>
<div class="admonition question">
<p class="admonition-title">Question</p>
<p>给定一二叉树的前序遍历 <code>preorder</code> 和中序遍历 <code>inorder</code> ,请从中构建二叉树,返回二叉树的根节点。假设二叉树中没有值重复的节点。</p>
<p>给定一二叉树的前序遍历 <code>preorder</code> 和中序遍历 <code>inorder</code> ,请从中构建二叉树,返回二叉树的根节点。假设二叉树中没有值重复的节点。</p>
</div>
<p><a class="glightbox" href="../build_binary_tree_problem.assets/build_tree_example.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="构建二叉树的示例数据" class="animation-figure" src="../build_binary_tree_problem.assets/build_tree_example.png" /></a></p>
<p align="center"> 图 12-5 &nbsp; 构建二叉树的示例数据 </p>
<h3 id="1">1. &nbsp; 判断是否为分治问题<a class="headerlink" href="#1" title="Permanent link">&para;</a></h3>
<p>原问题定义为从 <code>preorder</code><code>inorder</code> 构建二叉树,是一个典型的分治问题。</p>
<p>原问题定义为从 <code>preorder</code><code>inorder</code> 构建二叉树,是一个典型的分治问题。</p>
<ul>
<li><strong>问题可以分解</strong>:从分治的角度切入,我们可以将原问题划分为两个子问题:构建左子树、构建右子树,加上一步操作:初始化根节点。而对于每子树(子问题),我们仍然可以复用以上划分方法,将其划分为更小的子树(子问题),直至达到最小子问题(空子树)时终止。</li>
<li><strong>子问题是独立的</strong>:左子树和右子树是相互独立的,它们之间没有交集。在构建左子树时,我们只需关注中序遍历和前序遍历中与左子树对应的部分。右子树同理。</li>
<li><strong>问题可以分解</strong>:从分治的角度切入,我们可以将原问题划分为两个子问题:构建左子树、构建右子树,加上一步操作:初始化根节点。而对于每子树(子问题),我们仍然可以复用以上划分方法,将其划分为更小的子树(子问题),直至达到最小子问题(空子树)时终止。</li>
<li><strong>子问题是独立的</strong>:左子树和右子树是相互独立的,它们之间没有交集。在构建左子树时,我们只需关注中序遍历和前序遍历中与左子树对应的部分。右子树同理。</li>
<li><strong>子问题的解可以合并</strong>:一旦得到了左子树和右子树(子问题的解),我们就可以将它们链接到根节点上,得到原问题的解。</li>
</ul>
<h3 id="2">2. &nbsp; 如何划分子树<a class="headerlink" href="#2" title="Permanent link">&para;</a></h3>
<p>根据以上分析,这道题可以使用分治来求解<strong>但如何通过前序遍历 <code>preorder</code> 和中序遍历 <code>inorder</code> 来划分左子树和右子树呢</strong></p>
<p>根据定义,<code>preorder</code><code>inorder</code> 都可以划分为三个部分。</p>
<p>根据以上分析,这道题可以使用分治来求解,<strong>但如何通过前序遍历 <code>preorder</code> 和中序遍历 <code>inorder</code> 来划分左子树和右子树呢</strong></p>
<p>根据定义,<code>preorder</code><code>inorder</code> 都可以划分为三个部分。</p>
<ul>
<li>前序遍历:<code>[ 根节点 | 左子树 | 右子树 ]</code> ,例如图 12-5 的树对应 <code>[ 3 | 9 | 2 1 7 ]</code></li>
<li>中序遍历:<code>[ 左子树 | 根节点 右子树 ]</code> ,例如图 12-5 的树对应 <code>[ 9 | 3 | 1 2 7 ]</code></li>
@@ -3437,8 +3437,8 @@
<li>查找根节点 3 在 <code>inorder</code> 中的索引,利用该索引可将 <code>inorder</code> 划分为 <code>[ 9 | 3 1 2 7 ]</code></li>
<li>根据 <code>inorder</code> 划分结果,易得左子树和右子树的节点数量分别为 1 和 3 ,从而可将 <code>preorder</code> 划分为 <code>[ 3 | 9 | 2 1 7 ]</code></li>
</ol>
<p><a class="glightbox" href="../build_binary_tree_problem.assets/build_tree_preorder_inorder_division.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="在前序和中序遍历中划分子树" class="animation-figure" src="../build_binary_tree_problem.assets/build_tree_preorder_inorder_division.png" /></a></p>
<p align="center"> 图 12-6 &nbsp; 在前序和中序遍历中划分子树 </p>
<p><a class="glightbox" href="../build_binary_tree_problem.assets/build_tree_preorder_inorder_division.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="在前序遍历和中序遍历中划分子树" class="animation-figure" src="../build_binary_tree_problem.assets/build_tree_preorder_inorder_division.png" /></a></p>
<p align="center"> 图 12-6 &nbsp; 在前序遍历和中序遍历中划分子树 </p>
<h3 id="3">3. &nbsp; 基于变量描述子树区间<a class="headerlink" href="#3" title="Permanent link">&para;</a></h3>
<p>根据以上划分方法,<strong>我们已经得到根节点、左子树、右子树在 <code>preorder</code><code>inorder</code> 中的索引区间</strong>。而为了描述这些索引区间,我们需要借助几个指针变量。</p>
@@ -3448,7 +3448,7 @@
<li>将当前树在 <code>inorder</code> 中的索引区间记为 <span class="arithmatex">\([l, r]\)</span></li>
</ul>
<p>如表 12-1 所示,通过以上变量即可表示根节点在 <code>preorder</code> 中的索引,以及子树在 <code>inorder</code> 中的索引区间。</p>
<p align="center"> 表 12-1 &nbsp; 根节点和子树在前序和中序遍历中的索引 </p>
<p align="center"> 表 12-1 &nbsp; 根节点和子树在前序遍历和中序遍历中的索引 </p>
<div class="center-table">
<table>
@@ -3483,7 +3483,7 @@
<p align="center"> 图 12-7 &nbsp; 根节点和左右子树的索引区间表示 </p>
<h3 id="4">4. &nbsp; 代码实现<a class="headerlink" href="#4" title="Permanent link">&para;</a></h3>
<p>为了提升查询 <span class="arithmatex">\(m\)</span> 的效率,我们借助一个哈希表 <code>hmap</code> 来存储数组 <code>inorder</code> 中元素到索引的映射</p>
<p>为了提升查询 <span class="arithmatex">\(m\)</span> 的效率,我们借助一个哈希表 <code>hmap</code> 来存储数组 <code>inorder</code> 中元素到索引的映射</p>
<div class="tabbed-set tabbed-alternate" data-tabs="1:12"><input checked="checked" id="__tabbed_1_1" name="__tabbed_1" type="radio" /><input id="__tabbed_1_2" name="__tabbed_1" type="radio" /><input id="__tabbed_1_3" name="__tabbed_1" type="radio" /><input id="__tabbed_1_4" name="__tabbed_1" type="radio" /><input id="__tabbed_1_5" name="__tabbed_1" type="radio" /><input id="__tabbed_1_6" name="__tabbed_1" type="radio" /><input id="__tabbed_1_7" name="__tabbed_1" type="radio" /><input id="__tabbed_1_8" name="__tabbed_1" type="radio" /><input id="__tabbed_1_9" name="__tabbed_1" type="radio" /><input id="__tabbed_1_10" name="__tabbed_1" type="radio" /><input id="__tabbed_1_11" name="__tabbed_1" type="radio" /><input id="__tabbed_1_12" name="__tabbed_1" type="radio" /><div class="tabbed-labels"><label for="__tabbed_1_1">Python</label><label for="__tabbed_1_2">C++</label><label for="__tabbed_1_3">Java</label><label for="__tabbed_1_4">C#</label><label for="__tabbed_1_5">Go</label><label for="__tabbed_1_6">Swift</label><label for="__tabbed_1_7">JS</label><label for="__tabbed_1_8">TS</label><label for="__tabbed_1_9">Dart</label><label for="__tabbed_1_10">Rust</label><label for="__tabbed_1_11">C</label><label for="__tabbed_1_12">Zig</label></div>
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</div>
<p>图 12-8 展示了构建二叉树的递归过程,各个节点是在向下“递”的过程中建立的,而各条边(引用)是在向上“归”的过程中建立的。</p>
<p>图 12-8 展示了构建二叉树的递归过程,各个节点是在向下“递”的过程中建立的,而各条边(引用)是在向上“归”的过程中建立的。</p>
<div class="tabbed-set tabbed-alternate" data-tabs="2:9"><input checked="checked" id="__tabbed_2_1" name="__tabbed_2" type="radio" /><input id="__tabbed_2_2" name="__tabbed_2" type="radio" /><input id="__tabbed_2_3" name="__tabbed_2" type="radio" /><input id="__tabbed_2_4" name="__tabbed_2" type="radio" /><input id="__tabbed_2_5" name="__tabbed_2" type="radio" /><input id="__tabbed_2_6" name="__tabbed_2" type="radio" /><input id="__tabbed_2_7" name="__tabbed_2" type="radio" /><input id="__tabbed_2_8" name="__tabbed_2" type="radio" /><input id="__tabbed_2_9" name="__tabbed_2" type="radio" /><div class="tabbed-labels"><label for="__tabbed_2_1">&lt;1&gt;</label><label for="__tabbed_2_2">&lt;2&gt;</label><label for="__tabbed_2_3">&lt;3&gt;</label><label for="__tabbed_2_4">&lt;4&gt;</label><label for="__tabbed_2_5">&lt;5&gt;</label><label for="__tabbed_2_6">&lt;6&gt;</label><label for="__tabbed_2_7">&lt;7&gt;</label><label for="__tabbed_2_8">&lt;8&gt;</label><label for="__tabbed_2_9">&lt;9&gt;</label></div>
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<p align="center"> 图 12-9 &nbsp; 每个递归函数中的划分结果 </p>
<p>设树的节点数量为 <span class="arithmatex">\(n\)</span> ,初始化每一个节点(执行一个递归函数 <code>dfs()</code> )使用 <span class="arithmatex">\(O(1)\)</span> 时间。<strong>因此总体时间复杂度为 <span class="arithmatex">\(O(n)\)</span></strong></p>
<p>哈希表存储 <code>inorder</code> 元素到索引的映射,空间复杂度为 <span class="arithmatex">\(O(n)\)</span> 。最差情况下,即二叉树退化为链表时,递归深度达到 <span class="arithmatex">\(n\)</span> ,使用 <span class="arithmatex">\(O(n)\)</span> 的栈帧空间。<strong>因此总体空间复杂度为 <span class="arithmatex">\(O(n)\)</span></strong></p>
<p>哈希表存储 <code>inorder</code> 元素到索引的映射,空间复杂度为 <span class="arithmatex">\(O(n)\)</span>最差情况下,即二叉树退化为链表时,递归深度达到 <span class="arithmatex">\(n\)</span> ,使用 <span class="arithmatex">\(O(n)\)</span> 的栈帧空间。<strong>因此总体空间复杂度为 <span class="arithmatex">\(O(n)\)</span></strong></p>
<!-- Source file information -->
@@ -3452,21 +3452,21 @@
<h2 id="1211">12.1.1 &nbsp; 如何判断分治问题<a class="headerlink" href="#1211" title="Permanent link">&para;</a></h2>
<p>一个问题是否适合使用分治解决,通常可以参考以下几个判断依据。</p>
<ol>
<li><strong>问题可以分解</strong>:原问题可以分解成规模更小、类似的子问题,以及能够以相同方式递归地进行划分。</li>
<li><strong>子问题是独立的</strong>:子问题之间没有重叠,互相没有依赖,可以独立解决。</li>
<li><strong>子问题的解可以合并</strong>:原问题的解通过合并子问题的解得来。</li>
<li><strong>问题可以分解</strong>:原问题可以分解成规模更小、类似的子问题,以及能够以相同方式递归地进行划分。</li>
<li><strong>子问题是独立的</strong>:子问题之间没有重叠,互依赖,可以独立解决。</li>
<li><strong>子问题的解可以合并</strong>:原问题的解通过合并子问题的解得来。</li>
</ol>
<p>显然,归并排序满足以上三条判断依据</p>
<p>显然,归并排序满足以上三条判断依据。</p>
<ol>
<li><strong>问题可以分解</strong>:递归地将数组(原问题)划分为两个子数组(子问题)。</li>
<li><strong>问题可以分解</strong>:递归地将数组(原问题)划分为两个子数组(子问题)。</li>
<li><strong>子问题是独立的</strong>:每个子数组都可以独立地进行排序(子问题可以独立进行求解)。</li>
<li><strong>子问题的解可以合并</strong>:两个有序子数组(子问题的解)可以合并为一个有序数组(原问题的解)。</li>
<li><strong>子问题的解可以合并</strong>:两个有序子数组(子问题的解)可以合并为一个有序数组(原问题的解)。</li>
</ol>
<h2 id="1212">12.1.2 &nbsp; 通过分治提升效率<a class="headerlink" href="#1212" title="Permanent link">&para;</a></h2>
<p>分治不仅可以有效地解决算法问题,<strong>往往还可以带来算法效率的提升</strong>。在排序算法中,快速排序、归并排序、堆排序相较于选择、冒泡、插入排序更快,就是因为它们应用了分治策略。</p>
<p><strong>分治不仅可以有效地解决算法问题,往往还可以提升算法效率</strong>。在排序算法中,快速排序、归并排序、堆排序相较于选择、冒泡、插入排序更快,就是因为它们应用了分治策略。</p>
<p>那么,我们不禁发问:<strong>为什么分治可以提升算法效率,其底层逻辑是什么</strong>?换句话说,将大问题分解为多个子问题、解决子问题、将子问题的解合并为原问题的解,这几步的效率为什么比直接解决原问题的效率更高?这个问题可以从操作数量和并行计算两方面来讨论。</p>
<h3 id="1">1. &nbsp; 操作数量优化<a class="headerlink" href="#1" title="Permanent link">&para;</a></h3>
<p>以“冒泡排序”为例,其处理一个长度为 <span class="arithmatex">\(n\)</span> 的数组需要 <span class="arithmatex">\(O(n^2)\)</span> 时间。假设我们按照图 12-2 所示的方式,将数组从中点分为两个子数组,则划分需要 <span class="arithmatex">\(O(n)\)</span> 时间,排序每个子数组需要 <span class="arithmatex">\(O((n / 2)^2)\)</span> 时间,合并两个子数组需要 <span class="arithmatex">\(O(n)\)</span> 时间,总体时间复杂度为:</p>
<p>以“冒泡排序”为例,其处理一个长度为 <span class="arithmatex">\(n\)</span> 的数组需要 <span class="arithmatex">\(O(n^2)\)</span> 时间。假设我们按照图 12-2 所示的方式,将数组从中点分为两个子数组,则划分需要 <span class="arithmatex">\(O(n)\)</span> 时间,排序每个子数组需要 <span class="arithmatex">\(O((n / 2)^2)\)</span> 时间,合并两个子数组需要 <span class="arithmatex">\(O(n)\)</span> 时间,总体时间复杂度为:</p>
<div class="arithmatex">\[
O(n + (\frac{n}{2})^2 \times 2 + n) = O(\frac{n^2}{2} + 2n)
\]</div>
@@ -3482,33 +3482,33 @@ n(n - 4) &amp; &gt; 0
\end{aligned}
\]</div>
<p><strong>这意味着当 <span class="arithmatex">\(n &gt; 4\)</span> 时,划分后的操作数量更少,排序效率应该更高</strong>。请注意,划分后的时间复杂度仍然是平方阶 <span class="arithmatex">\(O(n^2)\)</span> ,只是复杂度中的常数项变小了。</p>
<p>进一步想,<strong>如果我们把子数组不断地再从中点划分为两个子数组</strong>,直至子数组只剩一个元素时停止划分呢?这种思路实际上就是“归并排序”,时间复杂度为 <span class="arithmatex">\(O(n \log n)\)</span></p>
<p>进一步想,<strong>如果我们把子数组不断地再从中点划分为两个子数组</strong>,直至子数组只剩一个元素时停止划分呢?这种思路实际上就是“归并排序”,时间复杂度为 <span class="arithmatex">\(O(n \log n)\)</span></p>
<p>再思考,<strong>如果我们多设置几个划分点</strong>,将原数组平均划分为 <span class="arithmatex">\(k\)</span> 个子数组呢?这种情况与“桶排序”非常类似,它非常适合排序海量数据,理论上时间复杂度可以达到 <span class="arithmatex">\(O(n + k)\)</span></p>
<h3 id="2">2. &nbsp; 并行计算优化<a class="headerlink" href="#2" title="Permanent link">&para;</a></h3>
<p>我们知道,分治生成的子问题是相互独立的,<strong>因此通常可以并行解决</strong>。也就是说,分治不仅可以降低算法的时间复杂度,<strong>还有利于操作系统的并行优化</strong></p>
<p>并行优化在多核或多处理器的环境中尤其有效,因为系统可以同时处理多个子问题,更加充分地利用计算资源,从而显著减少总体的运行时间。</p>
<p>比如在图 12-3 所示的“桶排序”中,我们将海量的数据平均分配到各个桶中,则可所有桶的排序任务分散到各个计算单元,完成后再进行结果合并。</p>
<p>比如在图 12-3 所示的“桶排序”中,我们将海量的数据平均分配到各个桶中,则可所有桶的排序任务分散到各个计算单元,完成后再合并结果</p>
<p><a class="glightbox" href="../divide_and_conquer.assets/divide_and_conquer_parallel_computing.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="桶排序的并行计算" class="animation-figure" src="../divide_and_conquer.assets/divide_and_conquer_parallel_computing.png" /></a></p>
<p align="center"> 图 12-3 &nbsp; 桶排序的并行计算 </p>
<h2 id="1213">12.1.3 &nbsp; 分治常见应用<a class="headerlink" href="#1213" title="Permanent link">&para;</a></h2>
<p>一方面,分治可以用来解决许多经典算法问题。</p>
<ul>
<li><strong>寻找最近点对</strong>:该算法首先将点集分成两部分,然后分别找出两部分中的最近点对,最后找出跨越两部分的最近点对。</li>
<li><strong>大整数乘法</strong>:例如 Karatsuba 算法,它将大整数乘法分解为几个较小的整数的乘法和加法。</li>
<li><strong>矩阵乘法</strong>:例如 Strassen 算法,它将大矩阵乘法分解为多个小矩阵的乘法和加法。</li>
<li><strong>汉诺塔问题</strong>:汉诺塔问题可以视为典型的分治策略,通过递归解决。</li>
<li><strong>求解逆序对</strong>:在一个序列中,如果前面的数字大于后面的数字,那么这两个数字构成一个逆序对。求解逆序对问题可以通过分治的思想,借助归并排序进行求解。</li>
<li><strong>寻找最近点对</strong>:该算法首先将点集分成两部分,然后分别找出两部分中的最近点对,最后找出跨越两部分的最近点对。</li>
<li><strong>大整数乘法</strong>:例如 Karatsuba 算法,它将大整数乘法分解为几个较小的整数的乘法和加法。</li>
<li><strong>矩阵乘法</strong>:例如 Strassen 算法,它将大矩阵乘法分解为多个小矩阵的乘法和加法。</li>
<li><strong>汉诺塔问题</strong>:汉诺塔问题可以通过递归解决,这是典型的分治策略应用</li>
<li><strong>求解逆序对</strong>:在一个序列中,如果前面的数字大于后面的数字,那么这两个数字构成一个逆序对。求解逆序对问题可以利用分治的思想,借助归并排序进行求解。</li>
</ul>
<p>另一方面,分治在算法和数据结构的设计中应用非常广泛。</p>
<ul>
<li><strong>二分查找</strong>:二分查找是将有序数组从中点索引分为两部分,然后根据目标值与中间元素值比较结果,决定排除哪一半区间,然后在剩余区间执行相同的二分操作。</li>
<li><strong>归并排序</strong>文章开头已介绍,不再赘述。</li>
<li><strong>快速排序</strong>:快速排序是选取一个基准值,然后把数组分为两个子数组,一个子数组的元素比基准值小,另一子数组的元素比基准值大,然后再对这两部分进行相同的划分操作,直至子数组只剩下一个元素。</li>
<li><strong>二分查找</strong>:二分查找是将有序数组从中点索引分为两部分,然后根据目标值与中间元素值比较结果,决定排除哪一半区间,在剩余区间执行相同的二分操作。</li>
<li><strong>归并排序</strong>本节开头已介绍,不再赘述。</li>
<li><strong>快速排序</strong>:快速排序是选取一个基准值,然后把数组分为两个子数组,一个子数组的元素比基准值小,另一子数组的元素比基准值大,再对这两部分进行相同的划分操作,直至子数组只剩下一个元素。</li>
<li><strong>桶排序</strong>:桶排序的基本思想是将数据分散到多个桶,然后对每个桶内的元素进行排序,最后将各个桶的元素依次取出,从而得到一个有序数组。</li>
<li><strong></strong>:例如二叉搜索树、AVL 树、红黑树、B 树、B+ 树等,它们的查找、插入和删除等操作都可以视为分治的应用。</li>
<li><strong></strong>:例如二叉搜索树、AVL 树、红黑树、B 树、B+ 树等,它们的查找、插入和删除等操作都可以视为分治策略的应用。</li>
<li><strong></strong>:堆是一种特殊的完全二叉树,其各种操作,如插入、删除和堆化,实际上都隐含了分治的思想。</li>
<li><strong>哈希表</strong>:虽然哈希表来并不直接应用分治,但某些哈希冲突解决策略间接应用了分治策略,例如,链式地址中的长链表会被转化为红黑树,以提升查询效率。</li>
<li><strong>哈希表</strong>:虽然哈希表来并不直接应用分治,但某些哈希冲突解决方案间接应用了分治策略,例如,链式地址中的长链表会被转化为红黑树,以提升查询效率。</li>
</ul>
<p>可以看出,<strong>分治是一种“润物细无声”的算法思想</strong>,隐含在各种算法与数据结构之中。</p>
@@ -3399,9 +3399,9 @@
<p>在归并排序和构建二叉树中,我们都是将原问题分解为两个规模为原问题一半的子问题。然而对于汉诺塔问题,我们采用不同的分解策略。</p>
<div class="admonition question">
<p class="admonition-title">Question</p>
<p>给定三根柱子,记为 <code>A</code><code>B</code><code>C</code> 。起始状态下,柱子 <code>A</code> 上套着 <span class="arithmatex">\(n\)</span> 个圆盘,它们从上到下按照从小到大的顺序排列。我们的任务是要把这 <span class="arithmatex">\(n\)</span> 个圆盘移到柱子 <code>C</code> 上,并保持它们的原有顺序不变。在移动圆盘的过程中,需要遵守以下规则。</p>
<p>给定三根柱子,记为 <code>A</code><code>B</code><code>C</code> 。起始状态下,柱子 <code>A</code> 上套着 <span class="arithmatex">\(n\)</span> 个圆盘,它们从上到下按照从小到大的顺序排列。我们的任务是要把这 <span class="arithmatex">\(n\)</span> 个圆盘移到柱子 <code>C</code> 上,并保持它们的原有顺序不变(如图 12-10 所示)。在移动圆盘的过程中,需要遵守以下规则。</p>
<ol>
<li>圆盘只能从一柱子顶部拿出,从另一柱子顶部放入。</li>
<li>圆盘只能从一柱子顶部拿出,从另一柱子顶部放入。</li>
<li>每次只能移动一个圆盘。</li>
<li>小圆盘必须时刻位于大圆盘之上。</li>
</ol>
@@ -3409,7 +3409,7 @@
<p><a class="glightbox" href="../hanota_problem.assets/hanota_example.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="汉诺塔问题示例" class="animation-figure" src="../hanota_problem.assets/hanota_example.png" /></a></p>
<p align="center"> 图 12-10 &nbsp; 汉诺塔问题示例 </p>
<p><strong>我们将规模为 <span class="arithmatex">\(i\)</span> 的汉诺塔问题记 <span class="arithmatex">\(f(i)\)</span></strong> 。例如 <span class="arithmatex">\(f(3)\)</span> 代表将 <span class="arithmatex">\(3\)</span> 个圆盘从 <code>A</code> 移动至 <code>C</code> 的汉诺塔问题。</p>
<p><strong>我们将规模为 <span class="arithmatex">\(i\)</span> 的汉诺塔问题记 <span class="arithmatex">\(f(i)\)</span></strong> 。例如 <span class="arithmatex">\(f(3)\)</span> 代表将 <span class="arithmatex">\(3\)</span> 个圆盘从 <code>A</code> 移动至 <code>C</code> 的汉诺塔问题。</p>
<h3 id="1">1. &nbsp; 考虑基本情况<a class="headerlink" href="#1" title="Permanent link">&para;</a></h3>
<p>如图 12-11 所示,对于问题 <span class="arithmatex">\(f(1)\)</span> ,即当只有一个圆盘时,我们将它直接从 <code>A</code> 移动至 <code>C</code> 即可。</p>
<div class="tabbed-set tabbed-alternate" data-tabs="1:2"><input checked="checked" id="__tabbed_1_1" name="__tabbed_1" type="radio" /><input id="__tabbed_1_2" name="__tabbed_1" type="radio" /><div class="tabbed-labels"><label for="__tabbed_1_1">&lt;1&gt;</label><label for="__tabbed_1_2">&lt;2&gt;</label></div>
@@ -3451,11 +3451,11 @@
<p>解决问题 <span class="arithmatex">\(f(2)\)</span> 的过程可总结为:<strong>将两个圆盘借助 <code>B</code><code>A</code> 移至 <code>C</code></strong> 。其中,<code>C</code> 称为目标柱、<code>B</code> 称为缓冲柱。</p>
<h3 id="2">2. &nbsp; 子问题分解<a class="headerlink" href="#2" title="Permanent link">&para;</a></h3>
<p>对于问题 <span class="arithmatex">\(f(3)\)</span> ,即当有三个圆盘时,情况变得稍微复杂了一些。</p>
<p>因为已知 <span class="arithmatex">\(f(1)\)</span><span class="arithmatex">\(f(2)\)</span> 的解,所以我们可从分治角度思考,<strong><code>A</code> 顶部的两个圆盘看一个整体</strong>,执行图 12-13 所示的步骤。这样三个圆盘就被顺利地从 <code>A</code><code>C</code> 了。</p>
<p>因为已知 <span class="arithmatex">\(f(1)\)</span><span class="arithmatex">\(f(2)\)</span> 的解,所以我们可从分治角度思考,<strong><code>A</code> 顶部的两个圆盘看一个整体</strong>,执行图 12-13 所示的步骤。这样三个圆盘就被顺利地从 <code>A</code> 移至 <code>C</code> 了。</p>
<ol>
<li><code>B</code> 为目标柱、<code>C</code> 为缓冲柱,将两个圆盘从 <code>A</code><code>B</code></li>
<li><code>B</code> 为目标柱、<code>C</code> 为缓冲柱,将两个圆盘从 <code>A</code> 移至 <code>B</code></li>
<li><code>A</code> 中剩余的一个圆盘从 <code>A</code> 直接移动至 <code>C</code></li>
<li><code>C</code> 为目标柱、<code>A</code> 为缓冲柱,将两个圆盘从 <code>B</code><code>C</code></li>
<li><code>C</code> 为目标柱、<code>A</code> 为缓冲柱,将两个圆盘从 <code>B</code> 移至 <code>C</code></li>
</ol>
<div class="tabbed-set tabbed-alternate" data-tabs="3:4"><input checked="checked" id="__tabbed_3_1" name="__tabbed_3" type="radio" /><input id="__tabbed_3_2" name="__tabbed_3" type="radio" /><input id="__tabbed_3_3" name="__tabbed_3" type="radio" /><input id="__tabbed_3_4" name="__tabbed_3" type="radio" /><div class="tabbed-labels"><label for="__tabbed_3_1">&lt;1&gt;</label><label for="__tabbed_3_2">&lt;2&gt;</label><label for="__tabbed_3_3">&lt;3&gt;</label><label for="__tabbed_3_4">&lt;4&gt;</label></div>
<div class="tabbed-content">
@@ -3475,19 +3475,19 @@
</div>
<p align="center"> 图 12-13 &nbsp; 规模为 3 问题的解 </p>
<p>本质上看,<strong>我们将问题 <span class="arithmatex">\(f(3)\)</span> 划分为两个子问题 <span class="arithmatex">\(f(2)\)</span> 和子问题 <span class="arithmatex">\(f(1)\)</span></strong> 。按顺序解决这三个子问题之后,原问题随之得到解决。这说明子问题是独立的,而且解可以合并</p>
<p>至此,我们可总结出图 12-14 所示的汉诺塔问题的分治策略:将原问题 <span class="arithmatex">\(f(n)\)</span> 划分为两个子问题 <span class="arithmatex">\(f(n-1)\)</span> 和一个子问题 <span class="arithmatex">\(f(1)\)</span> ,并按照以下顺序解决这三个子问题。</p>
<p>本质上看,<strong>我们将问题 <span class="arithmatex">\(f(3)\)</span> 划分为两个子问题 <span class="arithmatex">\(f(2)\)</span> 和子问题 <span class="arithmatex">\(f(1)\)</span></strong> 。按顺序解决这三个子问题之后,原问题随之得到解决。这说明子问题是独立的,而且解可以合并。</p>
<p>至此,我们可总结出图 12-14 所示的解决汉诺塔问题的分治策略:将原问题 <span class="arithmatex">\(f(n)\)</span> 划分为两个子问题 <span class="arithmatex">\(f(n-1)\)</span> 和一个子问题 <span class="arithmatex">\(f(1)\)</span> ,并按照以下顺序解决这三个子问题。</p>
<ol>
<li><span class="arithmatex">\(n-1\)</span> 个圆盘借助 <code>C</code><code>A</code> 移至 <code>B</code></li>
<li>将剩余 <span class="arithmatex">\(1\)</span> 个圆盘从 <code>A</code> 直接移至 <code>C</code></li>
<li><span class="arithmatex">\(n-1\)</span> 个圆盘借助 <code>A</code><code>B</code> 移至 <code>C</code></li>
</ol>
<p>对于这两个子问题 <span class="arithmatex">\(f(n-1)\)</span> <strong>可以通过相同的方式进行递归划分</strong>,直至达到最小子问题 <span class="arithmatex">\(f(1)\)</span> 。而 <span class="arithmatex">\(f(1)\)</span> 的解是已知的,只需一次移动操作即可。</p>
<p><a class="glightbox" href="../hanota_problem.assets/hanota_divide_and_conquer.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="汉诺塔问题的分治策略" class="animation-figure" src="../hanota_problem.assets/hanota_divide_and_conquer.png" /></a></p>
<p align="center"> 图 12-14 &nbsp; 汉诺塔问题的分治策略 </p>
<p><a class="glightbox" href="../hanota_problem.assets/hanota_divide_and_conquer.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="解决汉诺塔问题的分治策略" class="animation-figure" src="../hanota_problem.assets/hanota_divide_and_conquer.png" /></a></p>
<p align="center"> 图 12-14 &nbsp; 解决汉诺塔问题的分治策略 </p>
<h3 id="3">3. &nbsp; 代码实现<a class="headerlink" href="#3" title="Permanent link">&para;</a></h3>
<p>在代码中,我们声明一个递归函数 <code>dfs(i, src, buf, tar)</code> ,它的作用是将柱 <code>src</code> 顶部的 <span class="arithmatex">\(i\)</span> 个圆盘借助缓冲柱 <code>buf</code> 移动至目标柱 <code>tar</code> </p>
<p>在代码中,我们声明一个递归函数 <code>dfs(i, src, buf, tar)</code> ,它的作用是将柱 <code>src</code> 顶部的 <span class="arithmatex">\(i\)</span> 个圆盘借助缓冲柱 <code>buf</code> 移动至目标柱 <code>tar</code> </p>
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@@ -3499,7 +3499,7 @@
<a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a> <span class="n">tar</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">pan</span><span class="p">)</span>
<a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a>
<a id="__codelineno-0-8" name="__codelineno-0-8" href="#__codelineno-0-8"></a><span class="k">def</span> <span class="nf">dfs</span><span class="p">(</span><span class="n">i</span><span class="p">:</span> <span class="nb">int</span><span class="p">,</span> <span class="n">src</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">buf</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">tar</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]):</span>
<a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;求解汉诺塔问题 f(i)&quot;&quot;&quot;</span>
<a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;求解汉诺塔问题 f(i)&quot;&quot;&quot;</span>
<a id="__codelineno-0-10" name="__codelineno-0-10" href="#__codelineno-0-10"></a> <span class="c1"># 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-0-11" name="__codelineno-0-11" href="#__codelineno-0-11"></a> <span class="k">if</span> <span class="n">i</span> <span class="o">==</span> <span class="mi">1</span><span class="p">:</span>
<a id="__codelineno-0-12" name="__codelineno-0-12" href="#__codelineno-0-12"></a> <span class="n">move</span><span class="p">(</span><span class="n">src</span><span class="p">,</span> <span class="n">tar</span><span class="p">)</span>
@@ -3512,7 +3512,7 @@
<a id="__codelineno-0-19" name="__codelineno-0-19" href="#__codelineno-0-19"></a> <span class="n">dfs</span><span class="p">(</span><span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="p">,</span> <span class="n">buf</span><span class="p">,</span> <span class="n">src</span><span class="p">,</span> <span class="n">tar</span><span class="p">)</span>
<a id="__codelineno-0-20" name="__codelineno-0-20" href="#__codelineno-0-20"></a>
<a id="__codelineno-0-21" name="__codelineno-0-21" href="#__codelineno-0-21"></a><span class="k">def</span> <span class="nf">solve_hanota</span><span class="p">(</span><span class="n">A</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">B</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">],</span> <span class="n">C</span><span class="p">:</span> <span class="nb">list</span><span class="p">[</span><span class="nb">int</span><span class="p">]):</span>
<a id="__codelineno-0-22" name="__codelineno-0-22" href="#__codelineno-0-22"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;求解汉诺塔&quot;&quot;&quot;</span>
<a id="__codelineno-0-22" name="__codelineno-0-22" href="#__codelineno-0-22"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;求解汉诺塔问题&quot;&quot;&quot;</span>
<a id="__codelineno-0-23" name="__codelineno-0-23" href="#__codelineno-0-23"></a> <span class="n">n</span> <span class="o">=</span> <span class="nb">len</span><span class="p">(</span><span class="n">A</span><span class="p">)</span>
<a id="__codelineno-0-24" name="__codelineno-0-24" href="#__codelineno-0-24"></a> <span class="c1"># 将 A 顶部 n 个圆盘借助 B 移到 C</span>
<a id="__codelineno-0-25" name="__codelineno-0-25" href="#__codelineno-0-25"></a> <span class="n">dfs</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">A</span><span class="p">,</span> <span class="n">B</span><span class="p">,</span> <span class="n">C</span><span class="p">)</span>
@@ -3528,7 +3528,7 @@
<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w"> </span><span class="n">tar</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">pan</span><span class="p">);</span>
<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="p">}</span>
<a id="__codelineno-1-9" name="__codelineno-1-9" href="#__codelineno-1-9"></a>
<a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-1-11" name="__codelineno-1-11" href="#__codelineno-1-11"></a><span class="kt">void</span><span class="w"> </span><span class="nf">dfs</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">tar</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-1-12" name="__codelineno-1-12" href="#__codelineno-1-12"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-1-13" name="__codelineno-1-13" href="#__codelineno-1-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3543,7 +3543,7 @@
<a id="__codelineno-1-22" name="__codelineno-1-22" href="#__codelineno-1-22"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">);</span>
<a id="__codelineno-1-23" name="__codelineno-1-23" href="#__codelineno-1-23"></a><span class="p">}</span>
<a id="__codelineno-1-24" name="__codelineno-1-24" href="#__codelineno-1-24"></a>
<a id="__codelineno-1-25" name="__codelineno-1-25" href="#__codelineno-1-25"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-1-25" name="__codelineno-1-25" href="#__codelineno-1-25"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-1-26" name="__codelineno-1-26" href="#__codelineno-1-26"></a><span class="kt">void</span><span class="w"> </span><span class="nf">solveHanota</span><span class="p">(</span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="o">&amp;</span><span class="n">C</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-1-27" name="__codelineno-1-27" href="#__codelineno-1-27"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
<a id="__codelineno-1-28" name="__codelineno-1-28" href="#__codelineno-1-28"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3560,7 +3560,7 @@
<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a><span class="w"> </span><span class="n">tar</span><span class="p">.</span><span class="na">add</span><span class="p">(</span><span class="n">pan</span><span class="p">);</span>
<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="p">}</span>
<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a>
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a><span class="kt">void</span><span class="w"> </span><span class="nf">dfs</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">tar</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3575,7 +3575,7 @@
<a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">);</span>
<a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a><span class="p">}</span>
<a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a>
<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a><span class="kt">void</span><span class="w"> </span><span class="nf">solveHanota</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">C</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="na">size</span><span class="p">();</span>
<a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3593,7 +3593,7 @@
<a id="__codelineno-3-7" name="__codelineno-3-7" href="#__codelineno-3-7"></a><span class="w"> </span><span class="n">tar</span><span class="p">.</span><span class="n">Add</span><span class="p">(</span><span class="n">pan</span><span class="p">);</span>
<a id="__codelineno-3-8" name="__codelineno-3-8" href="#__codelineno-3-8"></a><span class="p">}</span>
<a id="__codelineno-3-9" name="__codelineno-3-9" href="#__codelineno-3-9"></a>
<a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-3-11" name="__codelineno-3-11" href="#__codelineno-3-11"></a><span class="k">void</span><span class="w"> </span><span class="nf">DFS</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">tar</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-3-12" name="__codelineno-3-12" href="#__codelineno-3-12"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-3-13" name="__codelineno-3-13" href="#__codelineno-3-13"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="m">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3608,7 +3608,7 @@
<a id="__codelineno-3-22" name="__codelineno-3-22" href="#__codelineno-3-22"></a><span class="w"> </span><span class="n">DFS</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">);</span>
<a id="__codelineno-3-23" name="__codelineno-3-23" href="#__codelineno-3-23"></a><span class="p">}</span>
<a id="__codelineno-3-24" name="__codelineno-3-24" href="#__codelineno-3-24"></a>
<a id="__codelineno-3-25" name="__codelineno-3-25" href="#__codelineno-3-25"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-3-25" name="__codelineno-3-25" href="#__codelineno-3-25"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-3-26" name="__codelineno-3-26" href="#__codelineno-3-26"></a><span class="k">void</span><span class="w"> </span><span class="nf">SolveHanota</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">C</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-3-27" name="__codelineno-3-27" href="#__codelineno-3-27"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">Count</span><span class="p">;</span>
<a id="__codelineno-3-28" name="__codelineno-3-28" href="#__codelineno-3-28"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3627,7 +3627,7 @@
<a id="__codelineno-4-8" name="__codelineno-4-8" href="#__codelineno-4-8"></a><span class="w"> </span><span class="nx">src</span><span class="p">.</span><span class="nx">Remove</span><span class="p">(</span><span class="nx">pan</span><span class="p">)</span>
<a id="__codelineno-4-9" name="__codelineno-4-9" href="#__codelineno-4-9"></a><span class="p">}</span>
<a id="__codelineno-4-10" name="__codelineno-4-10" href="#__codelineno-4-10"></a>
<a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-4-12" name="__codelineno-4-12" href="#__codelineno-4-12"></a><span class="kd">func</span><span class="w"> </span><span class="nx">dfsHanota</span><span class="p">(</span><span class="nx">i</span><span class="w"> </span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="p">,</span><span class="w"> </span><span class="nx">buf</span><span class="p">,</span><span class="w"> </span><span class="nx">tar</span><span class="w"> </span><span class="o">*</span><span class="nx">list</span><span class="p">.</span><span class="nx">List</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-4-13" name="__codelineno-4-13" href="#__codelineno-4-13"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-4-14" name="__codelineno-4-14" href="#__codelineno-4-14"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">{</span>
@@ -3642,7 +3642,7 @@
<a id="__codelineno-4-23" name="__codelineno-4-23" href="#__codelineno-4-23"></a><span class="w"> </span><span class="nx">dfsHanota</span><span class="p">(</span><span class="nx">i</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="nx">buf</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="p">,</span><span class="w"> </span><span class="nx">tar</span><span class="p">)</span>
<a id="__codelineno-4-24" name="__codelineno-4-24" href="#__codelineno-4-24"></a><span class="p">}</span>
<a id="__codelineno-4-25" name="__codelineno-4-25" href="#__codelineno-4-25"></a>
<a id="__codelineno-4-26" name="__codelineno-4-26" href="#__codelineno-4-26"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-4-26" name="__codelineno-4-26" href="#__codelineno-4-26"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-4-27" name="__codelineno-4-27" href="#__codelineno-4-27"></a><span class="kd">func</span><span class="w"> </span><span class="nx">solveHanota</span><span class="p">(</span><span class="nx">A</span><span class="p">,</span><span class="w"> </span><span class="nx">B</span><span class="p">,</span><span class="w"> </span><span class="nx">C</span><span class="w"> </span><span class="o">*</span><span class="nx">list</span><span class="p">.</span><span class="nx">List</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-4-28" name="__codelineno-4-28" href="#__codelineno-4-28"></a><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">A</span><span class="p">.</span><span class="nx">Len</span><span class="p">()</span>
<a id="__codelineno-4-29" name="__codelineno-4-29" href="#__codelineno-4-29"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3659,7 +3659,7 @@
<a id="__codelineno-5-6" name="__codelineno-5-6" href="#__codelineno-5-6"></a> <span class="n">tar</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">pan</span><span class="p">)</span>
<a id="__codelineno-5-7" name="__codelineno-5-7" href="#__codelineno-5-7"></a><span class="p">}</span>
<a id="__codelineno-5-8" name="__codelineno-5-8" href="#__codelineno-5-8"></a>
<a id="__codelineno-5-9" name="__codelineno-5-9" href="#__codelineno-5-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-5-9" name="__codelineno-5-9" href="#__codelineno-5-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-5-10" name="__codelineno-5-10" href="#__codelineno-5-10"></a><span class="kd">func</span> <span class="nf">dfs</span><span class="p">(</span><span class="n">i</span><span class="p">:</span> <span class="nb">Int</span><span class="p">,</span> <span class="n">src</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">],</span> <span class="n">buf</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">],</span> <span class="n">tar</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">])</span> <span class="p">{</span>
<a id="__codelineno-5-11" name="__codelineno-5-11" href="#__codelineno-5-11"></a> <span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-5-12" name="__codelineno-5-12" href="#__codelineno-5-12"></a> <span class="k">if</span> <span class="n">i</span> <span class="p">==</span> <span class="mi">1</span> <span class="p">{</span>
@@ -3674,7 +3674,7 @@
<a id="__codelineno-5-21" name="__codelineno-5-21" href="#__codelineno-5-21"></a> <span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="p">,</span> <span class="n">src</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">buf</span><span class="p">,</span> <span class="n">buf</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">src</span><span class="p">,</span> <span class="n">tar</span><span class="p">:</span> <span class="p">&amp;</span><span class="n">tar</span><span class="p">)</span>
<a id="__codelineno-5-22" name="__codelineno-5-22" href="#__codelineno-5-22"></a><span class="p">}</span>
<a id="__codelineno-5-23" name="__codelineno-5-23" href="#__codelineno-5-23"></a>
<a id="__codelineno-5-24" name="__codelineno-5-24" href="#__codelineno-5-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-5-24" name="__codelineno-5-24" href="#__codelineno-5-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-5-25" name="__codelineno-5-25" href="#__codelineno-5-25"></a><span class="kd">func</span> <span class="nf">solveHanota</span><span class="p">(</span><span class="n">A</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">],</span> <span class="n">B</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">],</span> <span class="n">C</span><span class="p">:</span> <span class="kr">inout</span> <span class="p">[</span><span class="nb">Int</span><span class="p">])</span> <span class="p">{</span>
<a id="__codelineno-5-26" name="__codelineno-5-26" href="#__codelineno-5-26"></a> <span class="kd">let</span> <span class="nv">n</span> <span class="p">=</span> <span class="n">A</span><span class="p">.</span><span class="bp">count</span>
<a id="__codelineno-5-27" name="__codelineno-5-27" href="#__codelineno-5-27"></a> <span class="c1">// 列表尾部是柱子顶部</span>
@@ -3692,7 +3692,7 @@
<a id="__codelineno-6-6" name="__codelineno-6-6" href="#__codelineno-6-6"></a><span class="w"> </span><span class="nx">tar</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">pan</span><span class="p">);</span>
<a id="__codelineno-6-7" name="__codelineno-6-7" href="#__codelineno-6-7"></a><span class="p">}</span>
<a id="__codelineno-6-8" name="__codelineno-6-8" href="#__codelineno-6-8"></a>
<a id="__codelineno-6-9" name="__codelineno-6-9" href="#__codelineno-6-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-6-9" name="__codelineno-6-9" href="#__codelineno-6-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-6-10" name="__codelineno-6-10" href="#__codelineno-6-10"></a><span class="kd">function</span><span class="w"> </span><span class="nx">dfs</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="p">,</span><span class="w"> </span><span class="nx">buf</span><span class="p">,</span><span class="w"> </span><span class="nx">tar</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-6-11" name="__codelineno-6-11" href="#__codelineno-6-11"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-6-12" name="__codelineno-6-12" href="#__codelineno-6-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">i</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="mf">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3707,7 +3707,7 @@
<a id="__codelineno-6-21" name="__codelineno-6-21" href="#__codelineno-6-21"></a><span class="w"> </span><span class="nx">dfs</span><span class="p">(</span><span class="nx">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</span><span class="p">,</span><span class="w"> </span><span class="nx">buf</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="p">,</span><span class="w"> </span><span class="nx">tar</span><span class="p">);</span>
<a id="__codelineno-6-22" name="__codelineno-6-22" href="#__codelineno-6-22"></a><span class="p">}</span>
<a id="__codelineno-6-23" name="__codelineno-6-23" href="#__codelineno-6-23"></a>
<a id="__codelineno-6-24" name="__codelineno-6-24" href="#__codelineno-6-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-6-24" name="__codelineno-6-24" href="#__codelineno-6-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-6-25" name="__codelineno-6-25" href="#__codelineno-6-25"></a><span class="kd">function</span><span class="w"> </span><span class="nx">solveHanota</span><span class="p">(</span><span class="nx">A</span><span class="p">,</span><span class="w"> </span><span class="nx">B</span><span class="p">,</span><span class="w"> </span><span class="nx">C</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-6-26" name="__codelineno-6-26" href="#__codelineno-6-26"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">A</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span>
<a id="__codelineno-6-27" name="__codelineno-6-27" href="#__codelineno-6-27"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3724,7 +3724,7 @@
<a id="__codelineno-7-6" name="__codelineno-7-6" href="#__codelineno-7-6"></a><span class="w"> </span><span class="nx">tar</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">pan</span><span class="p">);</span>
<a id="__codelineno-7-7" name="__codelineno-7-7" href="#__codelineno-7-7"></a><span class="p">}</span>
<a id="__codelineno-7-8" name="__codelineno-7-8" href="#__codelineno-7-8"></a>
<a id="__codelineno-7-9" name="__codelineno-7-9" href="#__codelineno-7-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-7-9" name="__codelineno-7-9" href="#__codelineno-7-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-7-10" name="__codelineno-7-10" href="#__codelineno-7-10"></a><span class="kd">function</span><span class="w"> </span><span class="nx">dfs</span><span class="p">(</span><span class="nx">i</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span><span class="w"> </span><span class="nx">buf</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span><span class="w"> </span><span class="nx">tar</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[])</span><span class="o">:</span><span class="w"> </span><span class="ow">void</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-7-11" name="__codelineno-7-11" href="#__codelineno-7-11"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-7-12" name="__codelineno-7-12" href="#__codelineno-7-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nx">i</span><span class="w"> </span><span class="o">===</span><span class="w"> </span><span class="mf">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3739,7 +3739,7 @@
<a id="__codelineno-7-21" name="__codelineno-7-21" href="#__codelineno-7-21"></a><span class="w"> </span><span class="nx">dfs</span><span class="p">(</span><span class="nx">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">1</span><span class="p">,</span><span class="w"> </span><span class="nx">buf</span><span class="p">,</span><span class="w"> </span><span class="nx">src</span><span class="p">,</span><span class="w"> </span><span class="nx">tar</span><span class="p">);</span>
<a id="__codelineno-7-22" name="__codelineno-7-22" href="#__codelineno-7-22"></a><span class="p">}</span>
<a id="__codelineno-7-23" name="__codelineno-7-23" href="#__codelineno-7-23"></a>
<a id="__codelineno-7-24" name="__codelineno-7-24" href="#__codelineno-7-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-7-24" name="__codelineno-7-24" href="#__codelineno-7-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-7-25" name="__codelineno-7-25" href="#__codelineno-7-25"></a><span class="kd">function</span><span class="w"> </span><span class="nx">solveHanota</span><span class="p">(</span><span class="nx">A</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span><span class="w"> </span><span class="nx">B</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[],</span><span class="w"> </span><span class="nx">C</span><span class="o">:</span><span class="w"> </span><span class="kt">number</span><span class="p">[])</span><span class="o">:</span><span class="w"> </span><span class="ow">void</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-7-26" name="__codelineno-7-26" href="#__codelineno-7-26"></a><span class="w"> </span><span class="kd">const</span><span class="w"> </span><span class="nx">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nx">A</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span>
<a id="__codelineno-7-27" name="__codelineno-7-27" href="#__codelineno-7-27"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3756,7 +3756,7 @@
<a id="__codelineno-8-6" name="__codelineno-8-6" href="#__codelineno-8-6"></a><span class="w"> </span><span class="n">tar</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">pan</span><span class="p">);</span>
<a id="__codelineno-8-7" name="__codelineno-8-7" href="#__codelineno-8-7"></a><span class="p">}</span>
<a id="__codelineno-8-8" name="__codelineno-8-8" href="#__codelineno-8-8"></a>
<a id="__codelineno-8-9" name="__codelineno-8-9" href="#__codelineno-8-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-8-9" name="__codelineno-8-9" href="#__codelineno-8-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-8-10" name="__codelineno-8-10" href="#__codelineno-8-10"></a><span class="kt">void</span><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">tar</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-8-11" name="__codelineno-8-11" href="#__codelineno-8-11"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-8-12" name="__codelineno-8-12" href="#__codelineno-8-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="m">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3771,7 +3771,7 @@
<a id="__codelineno-8-21" name="__codelineno-8-21" href="#__codelineno-8-21"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="m">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">);</span>
<a id="__codelineno-8-22" name="__codelineno-8-22" href="#__codelineno-8-22"></a><span class="p">}</span>
<a id="__codelineno-8-23" name="__codelineno-8-23" href="#__codelineno-8-23"></a>
<a id="__codelineno-8-24" name="__codelineno-8-24" href="#__codelineno-8-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-8-24" name="__codelineno-8-24" href="#__codelineno-8-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-8-25" name="__codelineno-8-25" href="#__codelineno-8-25"></a><span class="kt">void</span><span class="w"> </span><span class="n">solveHanota</span><span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">C</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-8-26" name="__codelineno-8-26" href="#__codelineno-8-26"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">length</span><span class="p">;</span>
<a id="__codelineno-8-27" name="__codelineno-8-27" href="#__codelineno-8-27"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3788,7 +3788,7 @@
<a id="__codelineno-9-6" name="__codelineno-9-6" href="#__codelineno-9-6"></a><span class="w"> </span><span class="n">tar</span><span class="p">.</span><span class="n">push</span><span class="p">(</span><span class="n">pan</span><span class="p">);</span>
<a id="__codelineno-9-7" name="__codelineno-9-7" href="#__codelineno-9-7"></a><span class="p">}</span>
<a id="__codelineno-9-8" name="__codelineno-9-8" href="#__codelineno-9-8"></a>
<a id="__codelineno-9-9" name="__codelineno-9-9" href="#__codelineno-9-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-9-9" name="__codelineno-9-9" href="#__codelineno-9-9"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-9-10" name="__codelineno-9-10" href="#__codelineno-9-10"></a><span class="k">fn</span> <span class="nf">dfs</span><span class="p">(</span><span class="n">i</span>: <span class="kt">i32</span><span class="p">,</span><span class="w"> </span><span class="n">src</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-9-11" name="__codelineno-9-11" href="#__codelineno-9-11"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-9-12" name="__codelineno-9-12" href="#__codelineno-9-12"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">{</span>
@@ -3803,7 +3803,7 @@
<a id="__codelineno-9-21" name="__codelineno-9-21" href="#__codelineno-9-21"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">);</span>
<a id="__codelineno-9-22" name="__codelineno-9-22" href="#__codelineno-9-22"></a><span class="p">}</span>
<a id="__codelineno-9-23" name="__codelineno-9-23" href="#__codelineno-9-23"></a>
<a id="__codelineno-9-24" name="__codelineno-9-24" href="#__codelineno-9-24"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-9-24" name="__codelineno-9-24" href="#__codelineno-9-24"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-9-25" name="__codelineno-9-25" href="#__codelineno-9-25"></a><span class="k">fn</span> <span class="nf">solve_hanota</span><span class="p">(</span><span class="n">A</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">B</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">C</span>: <span class="kp">&amp;</span><span class="nc">mut</span><span class="w"> </span><span class="nb">Vec</span><span class="o">&lt;</span><span class="kt">i32</span><span class="o">&gt;</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-9-26" name="__codelineno-9-26" href="#__codelineno-9-26"></a><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">len</span><span class="p">()</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="kt">i32</span><span class="p">;</span>
<a id="__codelineno-9-27" name="__codelineno-9-27" href="#__codelineno-9-27"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
@@ -3823,7 +3823,7 @@
<a id="__codelineno-10-9" name="__codelineno-10-9" href="#__codelineno-10-9"></a><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">tarSize</span><span class="p">)</span><span class="o">++</span><span class="p">;</span>
<a id="__codelineno-10-10" name="__codelineno-10-10" href="#__codelineno-10-10"></a><span class="p">}</span>
<a id="__codelineno-10-11" name="__codelineno-10-11" href="#__codelineno-10-11"></a>
<a id="__codelineno-10-12" name="__codelineno-10-12" href="#__codelineno-10-12"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-10-12" name="__codelineno-10-12" href="#__codelineno-10-12"></a><span class="cm">/* 求解汉诺塔问题 f(i) */</span>
<a id="__codelineno-10-13" name="__codelineno-10-13" href="#__codelineno-10-13"></a><span class="kt">void</span><span class="w"> </span><span class="nf">dfs</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">srcSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">bufSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">tar</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">tarSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-10-14" name="__codelineno-10-14" href="#__codelineno-10-14"></a><span class="w"> </span><span class="c1">// 若 src 只剩下一个圆盘,则直接将其移到 tar</span>
<a id="__codelineno-10-15" name="__codelineno-10-15" href="#__codelineno-10-15"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
@@ -3838,7 +3838,7 @@
<a id="__codelineno-10-24" name="__codelineno-10-24" href="#__codelineno-10-24"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">bufSize</span><span class="p">,</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">srcSize</span><span class="p">,</span><span class="w"> </span><span class="n">tar</span><span class="p">,</span><span class="w"> </span><span class="n">tarSize</span><span class="p">);</span>
<a id="__codelineno-10-25" name="__codelineno-10-25" href="#__codelineno-10-25"></a><span class="p">}</span>
<a id="__codelineno-10-26" name="__codelineno-10-26" href="#__codelineno-10-26"></a>
<a id="__codelineno-10-27" name="__codelineno-10-27" href="#__codelineno-10-27"></a><span class="cm">/* 求解汉诺塔 */</span>
<a id="__codelineno-10-27" name="__codelineno-10-27" href="#__codelineno-10-27"></a><span class="cm">/* 求解汉诺塔问题 */</span>
<a id="__codelineno-10-28" name="__codelineno-10-28" href="#__codelineno-10-28"></a><span class="kt">void</span><span class="w"> </span><span class="nf">solveHanota</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">ASize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">BSize</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">CSize</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-10-29" name="__codelineno-10-29" href="#__codelineno-10-29"></a><span class="w"> </span><span class="c1">// 将 A 顶部 n 个圆盘借助 B 移到 C</span>
<a id="__codelineno-10-30" name="__codelineno-10-30" href="#__codelineno-10-30"></a><span class="w"> </span><span class="n">dfs</span><span class="p">(</span><span class="o">*</span><span class="n">ASize</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">ASize</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">BSize</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">CSize</span><span class="p">);</span>
@@ -3855,13 +3855,13 @@
</div>
</div>
</div>
<p>如图 12-15 所示,汉诺塔问题形成一高度为 <span class="arithmatex">\(n\)</span> 的递归树,每个节点代表一个子问题对应一个开启的 <code>dfs()</code> 函数,<strong>因此时间复杂度为 <span class="arithmatex">\(O(2^n)\)</span> ,空间复杂度为 <span class="arithmatex">\(O(n)\)</span></strong></p>
<p>如图 12-15 所示,汉诺塔问题形成一高度为 <span class="arithmatex">\(n\)</span> 的递归树,每个节点代表一个子问题对应一个开启的 <code>dfs()</code> 函数,<strong>因此时间复杂度为 <span class="arithmatex">\(O(2^n)\)</span> ,空间复杂度为 <span class="arithmatex">\(O(n)\)</span></strong></p>
<p><a class="glightbox" href="../hanota_problem.assets/hanota_recursive_tree.png" data-type="image" data-width="100%" data-height="auto" data-desc-position="bottom"><img alt="汉诺塔问题的递归树" class="animation-figure" src="../hanota_problem.assets/hanota_recursive_tree.png" /></a></p>
<p align="center"> 图 12-15 &nbsp; 汉诺塔问题的递归树 </p>
<div class="admonition quote">
<p class="admonition-title">Quote</p>
<p>汉诺塔问题源自一古老的传说故事。在古印度的一个寺庙里,僧侣们有三根高大的钻石柱子,以及 <span class="arithmatex">\(64\)</span> 个大小不一的金圆盘。僧侣们不断地移动盘,他们相信在最后一个圆盘被正确放置的那一刻,这个世界就会结束。</p>
<p>汉诺塔问题源自一古老的传说。在古印度的一个寺庙里,僧侣们有三根高大的钻石柱子,以及 <span class="arithmatex">\(64\)</span> 个大小不一的金圆盘。僧侣们不断地移动盘,他们相信在最后一个圆盘被正确放置的那一刻,这个世界就会结束。</p>
<p>然而,即使僧侣们每秒钟移动一次,总共需要大约 <span class="arithmatex">\(2^{64} \approx 1.84×10^{19}\)</span> 秒,合约 <span class="arithmatex">\(5850\)</span> 亿年,远远超过了现在对宇宙年龄的估计。所以,倘若这个传说是真的,我们应该不需要担心世界末日的到来。</p>
</div>
@@ -3317,15 +3317,15 @@
<!-- Page content -->
<h1 id="125">12.5 &nbsp; 小结<a class="headerlink" href="#125" title="Permanent link">&para;</a></h1>
<ul>
<li>分治算法是一种常见的算法设计策略,包括分(划分)和治(合并)两个阶段,通常基于递归实现。</li>
<li>判断是否是分治算法问题的依据包括:问题能否分解、子问题是否独立、子问题是否可以被合并。</li>
<li>分治是一种常见的算法设计策略,包括分(划分)和治(合并)两个阶段,通常基于递归实现。</li>
<li>判断是否是分治算法问题的依据包括:问题能否分解、子问题是否独立、子问题能否合并。</li>
<li>归并排序是分治策略的典型应用,其递归地将数组划分为等长的两个子数组,直到只剩一个元素时开始逐层合并,从而完成排序。</li>
<li>引入分治策略往往可以带来算法效率的提升。一方面,分治策略减少了操作数量;另一方面,分治后有利于系统的并行优化。</li>
<li>引入分治策略往往可以提升算法效率。一方面,分治策略减少了操作数量;另一方面,分治后有利于系统的并行优化。</li>
<li>分治既可以解决许多算法问题,也广泛应用于数据结构与算法设计中,处处可见其身影。</li>
<li>相较于暴力搜索,自适应搜索效率更高。时间复杂度为 <span class="arithmatex">\(O(\log n)\)</span> 的搜索算法通常是基于分治策略实现的。</li>
<li>相较于暴力搜索,自适应搜索效率更高。时间复杂度为 <span class="arithmatex">\(O(\log n)\)</span> 的搜索算法通常是基于分治策略实现的。</li>
<li>二分查找是分治策略的另一个典型应用,它不包含将子问题的解进行合并的步骤。我们可以通过递归分治实现二分查找。</li>
<li>在构建二叉树问题中,构建树(原问题)可以划分为构建左子树和右子树(子问题),可以通过划分前序遍历和中序遍历的索引区间来实现。</li>
<li>在汉诺塔问题中,一个规模为 <span class="arithmatex">\(n\)</span> 的问题可以划分为两个规模为 <span class="arithmatex">\(n-1\)</span> 的子问题和一个规模为 <span class="arithmatex">\(1\)</span> 的子问题。按顺序解决这三个子问题后,原问题随之得到解决。</li>
<li>在构建二叉树问题中,构建树(原问题)可以划分为构建左子树和右子树(子问题),可以通过划分前序遍历和中序遍历的索引区间来实现。</li>
<li>在汉诺塔问题中,一个规模为 <span class="arithmatex">\(n\)</span> 的问题可以划分为两个规模为 <span class="arithmatex">\(n-1\)</span> 的子问题和一个规模为 <span class="arithmatex">\(1\)</span> 的子问题。按顺序解决这三个子问题后,原问题随之得到解决。</li>
</ul>
<!-- Source file information -->