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@@ -3433,10 +3433,10 @@
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</ol>
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<p>因此在能够解决问题的前提下,算法效率成为主要的评价维度,包括:</p>
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<ul>
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<li><strong>时间效率</strong>,即算法运行速度的快慢。</li>
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<li><strong>空间效率</strong>,即算法占用内存空间的大小。</li>
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<li><strong>时间效率</strong>:算法运行速度的快慢。</li>
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<li><strong>空间效率</strong>:算法占用内存空间的大小。</li>
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</ul>
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<p>简而言之,<strong>我们的目标是设计“既快又省”的数据结构与算法</strong>。而有效地评估算法效率至关重要,因为只有了解评价标准,我们才能对比分析各种算法,从而指导算法设计与优化过程。</p>
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<p>简而言之,<strong>我们的目标是设计“既快又省”的数据结构与算法</strong>。而有效地评估算法效率至关重要,因为只有这样我们才能将各种算法进行对比,从而指导算法设计与优化过程。</p>
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<p>效率评估方法主要分为两种:实际测试和理论估算。</p>
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<h2 id="211">2.1.1. 实际测试<a class="headerlink" href="#211" title="Permanent link">¶</a></h2>
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<p>假设我们现在有算法 <code>A</code> 和算法 <code>B</code> ,它们都能解决同一问题,现在需要对比这两个算法的效率。最直接的方法是找一台计算机,运行这两个算法,并监控记录它们的运行时间和内存占用情况。这种评估方式能够反映真实情况,但也存在较大局限性。</p>
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@@ -3445,12 +3445,12 @@
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<h2 id="212">2.1.2. 理论估算<a class="headerlink" href="#212" title="Permanent link">¶</a></h2>
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<p>由于实际测试具有较大的局限性,我们可以考虑仅通过一些计算来评估算法的效率。这种估算方法被称为「渐近复杂度分析 Asymptotic Complexity Analysis」,简称为「复杂度分析」。</p>
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<p><strong>复杂度分析评估的是算法运行效率随着输入数据量增多时的增长趋势</strong>。这个定义有些拗口,我们可以将其分为三个重点来理解:</p>
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<ul>
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<ol>
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<li>“算法运行效率”可分为运行时间和占用空间两部分,与之对应地,复杂度可分为「时间复杂度 Time Complexity」和「空间复杂度 Space Complexity」。</li>
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<li>“随着输入数据量增多时”表示复杂度与输入数据量有关,反映了算法运行效率与输入数据量之间的关系。</li>
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<li>“随着输入数据量增多时”意味着复杂度反映了算法运行效率与输入数据量之间的关系。</li>
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<li>“增长趋势”表示复杂度分析关注的是算法时间与空间的增长趋势,而非具体的运行时间或占用空间。</li>
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</ul>
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<p><strong>复杂度分析克服了实际测试方法的弊端</strong>。首先,它独立于测试环境,因此分析结果适用于所有运行平台。其次,它可以体现不同数据量下的算法效率,尤其是在大数据量下的算法性能。</p>
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</ol>
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<p><strong>复杂度分析克服了实际测试方法的弊端</strong>。首先,它独立于测试环境,分析结果适用于所有运行平台。其次,它可以体现不同数据量下的算法效率,尤其是在大数据量下的算法性能。</p>
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<p>如果你对复杂度分析的概念仍感到困惑,无需担心,我们会在后续章节详细介绍。</p>
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<h2 id="213">2.1.3. 复杂度的重要性<a class="headerlink" href="#213" title="Permanent link">¶</a></h2>
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<p>复杂度分析为我们提供了一把评估算法效率的“标尺”,帮助我们衡量了执行某个算法所需的时间和空间资源,并使我们能够对比不同算法之间的效率。</p>
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@@ -3539,7 +3539,7 @@
|
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</ul>
|
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<p>因此在分析一段程序的空间复杂度时,<strong>我们通常统计暂存数据、输出数据、栈帧空间三部分</strong>。</p>
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<p><img alt="算法使用的相关空间" src="../space_complexity.assets/space_types.png" /></p>
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<p align="center"> Fig. 算法使用的相关空间 </p>
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<p align="center"> 图:算法使用的相关空间 </p>
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<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">Java</label><label for="__tabbed_1_2">C++</label><label for="__tabbed_1_3">Python</label><label for="__tabbed_1_4">Go</label><label for="__tabbed_1_5">JS</label><label for="__tabbed_1_6">TS</label><label for="__tabbed_1_7">C</label><label for="__tabbed_1_8">C#</label><label for="__tabbed_1_9">Swift</label><label for="__tabbed_1_10">Zig</label><label for="__tabbed_1_11">Dart</label><label for="__tabbed_1_12">Rust</label></div>
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<div class="tabbed-content">
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@@ -3594,7 +3594,7 @@
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<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="w"> </span><span class="sd">"""类"""</span>
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<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a> <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">:</span> <span class="nb">int</span><span class="p">):</span>
|
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<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a> <span class="bp">self</span><span class="o">.</span><span class="n">val</span><span class="p">:</span> <span class="nb">int</span> <span class="o">=</span> <span class="n">x</span> <span class="c1"># 节点值</span>
|
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<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a> <span class="bp">self</span><span class="o">.</span><span class="n">next</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">Node</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span> <span class="c1"># 指向下一节点的指针(引用)</span>
|
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<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a> <span class="bp">self</span><span class="o">.</span><span class="n">next</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">Node</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span> <span class="c1"># 指向下一节点的引用</span>
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<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a>
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<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="k">def</span> <span class="nf">function</span><span class="p">()</span> <span class="o">-></span> <span class="nb">int</span><span class="p">:</span>
|
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<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a><span class="w"> </span><span class="sd">"""函数"""</span>
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@@ -4115,7 +4115,7 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
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\end{aligned}
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\]</div>
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<p><img alt="空间复杂度的常见类型" src="../space_complexity.assets/space_complexity_common_types.png" /></p>
|
||||
<p align="center"> Fig. 空间复杂度的常见类型 </p>
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||||
<p align="center"> 图:空间复杂度的常见类型 </p>
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<div class="admonition tip">
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<p class="admonition-title">Tip</p>
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@@ -4390,8 +4390,8 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
|
||||
<a id="__codelineno-46-9" name="__codelineno-46-9" href="#__codelineno-46-9"></a><span class="w"> </span><span class="c1">// 常量、变量、对象占用 O(1) 空间</span>
|
||||
<a id="__codelineno-46-10" name="__codelineno-46-10" href="#__codelineno-46-10"></a><span class="w"> </span><span class="kd">final</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span>
|
||||
<a id="__codelineno-46-11" name="__codelineno-46-11" href="#__codelineno-46-11"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span>
|
||||
<a id="__codelineno-46-12" name="__codelineno-46-12" href="#__codelineno-46-12"></a>
|
||||
<a id="__codelineno-46-13" name="__codelineno-46-13" href="#__codelineno-46-13"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">nums</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">filled</span><span class="p">(</span><span class="m">10000</span><span class="p">,</span><span class="w"> </span><span class="m">0</span><span class="p">);</span>
|
||||
<a id="__codelineno-46-12" name="__codelineno-46-12" href="#__codelineno-46-12"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">nums</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">filled</span><span class="p">(</span><span class="m">10000</span><span class="p">,</span><span class="w"> </span><span class="m">0</span><span class="p">);</span>
|
||||
<a id="__codelineno-46-13" name="__codelineno-46-13" href="#__codelineno-46-13"></a><span class="w"> </span><span class="n">ListNode</span><span class="w"> </span><span class="n">node</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ListNode</span><span class="p">(</span><span class="m">0</span><span class="p">);</span>
|
||||
<a id="__codelineno-46-14" name="__codelineno-46-14" href="#__codelineno-46-14"></a><span class="w"> </span><span class="c1">// 循环中的变量占用 O(1) 空间</span>
|
||||
<a id="__codelineno-46-15" name="__codelineno-46-15" href="#__codelineno-46-15"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kd">var</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-46-16" name="__codelineno-46-16" href="#__codelineno-46-16"></a><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span>
|
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@@ -4796,7 +4796,7 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
|
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</div>
|
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</div>
|
||||
<p><img alt="递归函数产生的线性阶空间复杂度" src="../space_complexity.assets/space_complexity_recursive_linear.png" /></p>
|
||||
<p align="center"> Fig. 递归函数产生的线性阶空间复杂度 </p>
|
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<p align="center"> 图:递归函数产生的线性阶空间复杂度 </p>
|
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|
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<h3 id="on2">平方阶 <span class="arithmatex">\(O(n^2)\)</span><a class="headerlink" href="#on2" title="Permanent link">¶</a></h3>
|
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<p>平方阶常见于矩阵和图,元素数量与 <span class="arithmatex">\(n\)</span> 成平方关系。</p>
|
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@@ -4962,15 +4962,14 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
|
||||
<a id="__codelineno-82-4" name="__codelineno-82-4" href="#__codelineno-82-4"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">>></span><span class="w"> </span><span class="n">numMatrix</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="n">_</span><span class="p">)</span><span class="w"> </span><span class="o">=></span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">filled</span><span class="p">(</span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="m">0</span><span class="p">));</span>
|
||||
<a id="__codelineno-82-5" name="__codelineno-82-5" href="#__codelineno-82-5"></a><span class="w"> </span><span class="c1">// 二维列表占用 O(n^2) 空间</span>
|
||||
<a id="__codelineno-82-6" name="__codelineno-82-6" href="#__codelineno-82-6"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">>></span><span class="w"> </span><span class="n">numList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
|
||||
<a id="__codelineno-82-7" name="__codelineno-82-7" href="#__codelineno-82-7"></a>
|
||||
<a id="__codelineno-82-8" name="__codelineno-82-8" href="#__codelineno-82-8"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kd">var</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-82-9" name="__codelineno-82-9" href="#__codelineno-82-9"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">tmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
|
||||
<a id="__codelineno-82-10" name="__codelineno-82-10" href="#__codelineno-82-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-82-11" name="__codelineno-82-11" href="#__codelineno-82-11"></a><span class="w"> </span><span class="n">tmp</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="m">0</span><span class="p">);</span>
|
||||
<a id="__codelineno-82-12" name="__codelineno-82-12" href="#__codelineno-82-12"></a><span class="w"> </span><span class="p">}</span>
|
||||
<a id="__codelineno-82-13" name="__codelineno-82-13" href="#__codelineno-82-13"></a><span class="w"> </span><span class="n">numList</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">tmp</span><span class="p">);</span>
|
||||
<a id="__codelineno-82-14" name="__codelineno-82-14" href="#__codelineno-82-14"></a><span class="w"> </span><span class="p">}</span>
|
||||
<a id="__codelineno-82-15" name="__codelineno-82-15" href="#__codelineno-82-15"></a><span class="p">}</span>
|
||||
<a id="__codelineno-82-7" name="__codelineno-82-7" href="#__codelineno-82-7"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kd">var</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-82-8" name="__codelineno-82-8" href="#__codelineno-82-8"></a><span class="w"> </span><span class="n">List</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">tmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[];</span>
|
||||
<a id="__codelineno-82-9" name="__codelineno-82-9" href="#__codelineno-82-9"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="m">0</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">n</span><span class="p">;</span><span class="w"> </span><span class="n">j</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-82-10" name="__codelineno-82-10" href="#__codelineno-82-10"></a><span class="w"> </span><span class="n">tmp</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="m">0</span><span class="p">);</span>
|
||||
<a id="__codelineno-82-11" name="__codelineno-82-11" href="#__codelineno-82-11"></a><span class="w"> </span><span class="p">}</span>
|
||||
<a id="__codelineno-82-12" name="__codelineno-82-12" href="#__codelineno-82-12"></a><span class="w"> </span><span class="n">numList</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">tmp</span><span class="p">);</span>
|
||||
<a id="__codelineno-82-13" name="__codelineno-82-13" href="#__codelineno-82-13"></a><span class="w"> </span><span class="p">}</span>
|
||||
<a id="__codelineno-82-14" name="__codelineno-82-14" href="#__codelineno-82-14"></a><span class="p">}</span>
|
||||
</code></pre></div>
|
||||
</div>
|
||||
<div class="tabbed-block">
|
||||
@@ -5132,7 +5131,7 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="递归函数产生的平方阶空间复杂度" src="../space_complexity.assets/space_complexity_recursive_quadratic.png" /></p>
|
||||
<p align="center"> Fig. 递归函数产生的平方阶空间复杂度 </p>
|
||||
<p align="center"> 图:递归函数产生的平方阶空间复杂度 </p>
|
||||
|
||||
<h3 id="o2n">指数阶 <span class="arithmatex">\(O(2^n)\)</span><a class="headerlink" href="#o2n" title="Permanent link">¶</a></h3>
|
||||
<p>指数阶常见于二叉树。高度为 <span class="arithmatex">\(n\)</span> 的「满二叉树」的节点数量为 <span class="arithmatex">\(2^n - 1\)</span> ,占用 <span class="arithmatex">\(O(2^n)\)</span> 空间。</p>
|
||||
@@ -5281,7 +5280,7 @@ O(1) < O(\log n) < O(n) < O(n^2) < O(2^n) \newline
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="满二叉树产生的指数阶空间复杂度" src="../space_complexity.assets/space_complexity_exponential.png" /></p>
|
||||
<p align="center"> Fig. 满二叉树产生的指数阶空间复杂度 </p>
|
||||
<p align="center"> 图:满二叉树产生的指数阶空间复杂度 </p>
|
||||
|
||||
<h3 id="olog-n">对数阶 <span class="arithmatex">\(O(\log n)\)</span><a class="headerlink" href="#olog-n" title="Permanent link">¶</a></h3>
|
||||
<p>对数阶常见于分治算法和数据类型转换等。</p>
|
||||
|
||||
@@ -3985,7 +3985,7 @@
|
||||
<p>算法 <code>B</code> 中的打印操作需要循环 <span class="arithmatex">\(n\)</span> 次,算法运行时间随着 <span class="arithmatex">\(n\)</span> 增大呈线性增长。此算法的时间复杂度被称为「线性阶」。</p>
|
||||
<p>算法 <code>C</code> 中的打印操作需要循环 <span class="arithmatex">\(1000000\)</span> 次,虽然运行时间很长,但它与输入数据大小 <span class="arithmatex">\(n\)</span> 无关。因此 <code>C</code> 的时间复杂度和 <code>A</code> 相同,仍为「常数阶」。</p>
|
||||
<p><img alt="算法 A, B, C 的时间增长趋势" src="../time_complexity.assets/time_complexity_simple_example.png" /></p>
|
||||
<p align="center"> Fig. 算法 A, B, C 的时间增长趋势 </p>
|
||||
<p align="center"> 图:算法 A, B, C 的时间增长趋势 </p>
|
||||
|
||||
<p>相较于直接统计算法运行时间,时间复杂度分析有哪些特点呢?</p>
|
||||
<p><strong>时间复杂度能够有效评估算法效率</strong>。例如,算法 <code>B</code> 的运行时间呈线性增长,在 <span class="arithmatex">\(n > 1\)</span> 时比算法 <code>A</code> 更慢,在 <span class="arithmatex">\(n > 1000000\)</span> 时比算法 <code>C</code> 更慢。事实上,只要输入数据大小 <span class="arithmatex">\(n\)</span> 足够大,复杂度为“常数阶”的算法一定优于“线性阶”的算法,这正是时间增长趋势所表达的含义。</p>
|
||||
@@ -4151,7 +4151,7 @@ T(n) = O(f(n))
|
||||
$$</p>
|
||||
</div>
|
||||
<p><img alt="函数的渐近上界" src="../time_complexity.assets/asymptotic_upper_bound.png" /></p>
|
||||
<p align="center"> Fig. 函数的渐近上界 </p>
|
||||
<p align="center"> 图:函数的渐近上界 </p>
|
||||
|
||||
<p>也就是说,计算渐近上界就是寻找一个函数 <span class="arithmatex">\(f(n)\)</span> ,使得当 <span class="arithmatex">\(n\)</span> 趋向于无穷大时,<span class="arithmatex">\(T(n)\)</span> 和 <span class="arithmatex">\(f(n)\)</span> 处于相同的增长级别,仅相差一个常数项 <span class="arithmatex">\(c\)</span> 的倍数。</p>
|
||||
<h2 id="223">2.2.3. 推算方法<a class="headerlink" href="#223" title="Permanent link">¶</a></h2>
|
||||
@@ -4409,7 +4409,7 @@ O(1) < O(\log n) < O(n) < O(n \log n) < O(n^2) < O(2^n) < O(n!
|
||||
\end{aligned}
|
||||
\]</div>
|
||||
<p><img alt="时间复杂度的常见类型" src="../time_complexity.assets/time_complexity_common_types.png" /></p>
|
||||
<p align="center"> Fig. 时间复杂度的常见类型 </p>
|
||||
<p align="center"> 图:时间复杂度的常见类型 </p>
|
||||
|
||||
<div class="admonition tip">
|
||||
<p class="admonition-title">Tip</p>
|
||||
@@ -5013,7 +5013,7 @@ O(1) < O(\log n) < O(n) < O(n \log n) < O(n^2) < O(2^n) < O(n!
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="常数阶、线性阶、平方阶的时间复杂度" src="../time_complexity.assets/time_complexity_constant_linear_quadratic.png" /></p>
|
||||
<p align="center"> Fig. 常数阶、线性阶、平方阶的时间复杂度 </p>
|
||||
<p align="center"> 图:常数阶、线性阶、平方阶的时间复杂度 </p>
|
||||
|
||||
<p>以「冒泡排序」为例,外层循环执行 <span class="arithmatex">\(n - 1\)</span> 次,内层循环执行 <span class="arithmatex">\(n-1, n-2, \cdots, 2, 1\)</span> 次,平均为 <span class="arithmatex">\(\frac{n}{2}\)</span> 次,因此时间复杂度为 <span class="arithmatex">\(O(n^2)\)</span> 。</p>
|
||||
<div class="arithmatex">\[
|
||||
@@ -5477,7 +5477,7 @@ O((n - 1) \frac{n}{2}) = O(n^2)
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="指数阶的时间复杂度" src="../time_complexity.assets/time_complexity_exponential.png" /></p>
|
||||
<p align="center"> Fig. 指数阶的时间复杂度 </p>
|
||||
<p align="center"> 图:指数阶的时间复杂度 </p>
|
||||
|
||||
<p>在实际算法中,指数阶常出现于递归函数。例如以下代码,其递归地一分为二,经过 <span class="arithmatex">\(n\)</span> 次分裂后停止。</p>
|
||||
<div class="tabbed-set tabbed-alternate" data-tabs="11:12"><input checked="checked" id="__tabbed_11_1" name="__tabbed_11" type="radio" /><input id="__tabbed_11_2" name="__tabbed_11" type="radio" /><input id="__tabbed_11_3" name="__tabbed_11" type="radio" /><input id="__tabbed_11_4" name="__tabbed_11" type="radio" /><input id="__tabbed_11_5" name="__tabbed_11" type="radio" /><input id="__tabbed_11_6" name="__tabbed_11" type="radio" /><input id="__tabbed_11_7" name="__tabbed_11" type="radio" /><input id="__tabbed_11_8" name="__tabbed_11" type="radio" /><input id="__tabbed_11_9" name="__tabbed_11" type="radio" /><input id="__tabbed_11_10" name="__tabbed_11" type="radio" /><input id="__tabbed_11_11" name="__tabbed_11" type="radio" /><input id="__tabbed_11_12" name="__tabbed_11" type="radio" /><div class="tabbed-labels"><label for="__tabbed_11_1">Java</label><label for="__tabbed_11_2">C++</label><label for="__tabbed_11_3">Python</label><label for="__tabbed_11_4">Go</label><label for="__tabbed_11_5">JS</label><label for="__tabbed_11_6">TS</label><label for="__tabbed_11_7">C</label><label for="__tabbed_11_8">C#</label><label for="__tabbed_11_9">Swift</label><label for="__tabbed_11_10">Zig</label><label for="__tabbed_11_11">Dart</label><label for="__tabbed_11_12">Rust</label></div>
|
||||
@@ -5742,7 +5742,7 @@ O((n - 1) \frac{n}{2}) = O(n^2)
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="对数阶的时间复杂度" src="../time_complexity.assets/time_complexity_logarithmic.png" /></p>
|
||||
<p align="center"> Fig. 对数阶的时间复杂度 </p>
|
||||
<p align="center"> 图:对数阶的时间复杂度 </p>
|
||||
|
||||
<p>与指数阶类似,对数阶也常出现于递归函数。以下代码形成了一个高度为 <span class="arithmatex">\(\log_2 n\)</span> 的递归树。</p>
|
||||
<div class="tabbed-set tabbed-alternate" data-tabs="13:12"><input checked="checked" id="__tabbed_13_1" name="__tabbed_13" type="radio" /><input id="__tabbed_13_2" name="__tabbed_13" type="radio" /><input id="__tabbed_13_3" name="__tabbed_13" type="radio" /><input id="__tabbed_13_4" name="__tabbed_13" type="radio" /><input id="__tabbed_13_5" name="__tabbed_13" type="radio" /><input id="__tabbed_13_6" name="__tabbed_13" type="radio" /><input id="__tabbed_13_7" name="__tabbed_13" type="radio" /><input id="__tabbed_13_8" name="__tabbed_13" type="radio" /><input id="__tabbed_13_9" name="__tabbed_13" type="radio" /><input id="__tabbed_13_10" name="__tabbed_13" type="radio" /><input id="__tabbed_13_11" name="__tabbed_13" type="radio" /><input id="__tabbed_13_12" name="__tabbed_13" type="radio" /><div class="tabbed-labels"><label for="__tabbed_13_1">Java</label><label for="__tabbed_13_2">C++</label><label for="__tabbed_13_3">Python</label><label for="__tabbed_13_4">Go</label><label for="__tabbed_13_5">JS</label><label for="__tabbed_13_6">TS</label><label for="__tabbed_13_7">C</label><label for="__tabbed_13_8">C#</label><label for="__tabbed_13_9">Swift</label><label for="__tabbed_13_10">Zig</label><label for="__tabbed_13_11">Dart</label><label for="__tabbed_13_12">Rust</label></div>
|
||||
@@ -6021,7 +6021,7 @@ O((n - 1) \frac{n}{2}) = O(n^2)
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="线性对数阶的时间复杂度" src="../time_complexity.assets/time_complexity_logarithmic_linear.png" /></p>
|
||||
<p align="center"> Fig. 线性对数阶的时间复杂度 </p>
|
||||
<p align="center"> 图:线性对数阶的时间复杂度 </p>
|
||||
|
||||
<h3 id="on_1">阶乘阶 <span class="arithmatex">\(O(n!)\)</span><a class="headerlink" href="#on_1" title="Permanent link">¶</a></h3>
|
||||
<p>阶乘阶对应数学上的“全排列”问题。给定 <span class="arithmatex">\(n\)</span> 个互不重复的元素,求其所有可能的排列方案,方案数量为:</p>
|
||||
@@ -6198,7 +6198,7 @@ n! = n \times (n - 1) \times (n - 2) \times \cdots \times 2 \times 1
|
||||
</div>
|
||||
</div>
|
||||
<p><img alt="阶乘阶的时间复杂度" src="../time_complexity.assets/time_complexity_factorial.png" /></p>
|
||||
<p align="center"> Fig. 阶乘阶的时间复杂度 </p>
|
||||
<p align="center"> 图:阶乘阶的时间复杂度 </p>
|
||||
|
||||
<p>请注意,因为 <span class="arithmatex">\(n! > 2^n\)</span> ,所以阶乘阶比指数阶增长地更快,在 <span class="arithmatex">\(n\)</span> 较大时也是不可接受的。</p>
|
||||
<h2 id="225">2.2.5. 最差、最佳、平均时间复杂度<a class="headerlink" href="#225" title="Permanent link">¶</a></h2>
|
||||
|
||||
Reference in New Issue
Block a user