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@@ -1819,7 +1819,7 @@ G & = \{ V, E \} \newline
|
||||
<p><img alt="链表、树、图之间的关系" src="../graph.assets/linkedlist_tree_graph.png" /></p>
|
||||
<p align="center"> Fig. 链表、树、图之间的关系 </p>
|
||||
|
||||
<p>那么,图与其他数据结构的关系是什么?如果我们把「顶点」看作结点,把「边」看作连接各个结点的指针,则可将「图」看作是一种从「链表」拓展而来的数据结构。<strong>相较于线性关系(链表)和分治关系(树),网络关系(图)的自由度更高,从而更为复杂</strong>。</p>
|
||||
<p>那么,图与其他数据结构的关系是什么?如果我们把「顶点」看作节点,把「边」看作连接各个节点的指针,则可将「图」看作是一种从「链表」拓展而来的数据结构。<strong>相较于线性关系(链表)和分治关系(树),网络关系(图)的自由度更高,从而更为复杂</strong>。</p>
|
||||
<h2 id="911">9.1.1. 图常见类型<a class="headerlink" href="#911" title="Permanent link">¶</a></h2>
|
||||
<p>根据边是否具有方向,可分为「无向图 Undirected Graph」和「有向图 Directed Graph」。</p>
|
||||
<ul>
|
||||
@@ -1863,7 +1863,7 @@ G & = \{ V, E \} \newline
|
||||
</ul>
|
||||
<p>使用邻接矩阵表示图时,我们可以直接访问矩阵元素以获取边,因此增删查操作的效率很高,时间复杂度均为 <span class="arithmatex">\(O(1)\)</span> 。然而,矩阵的空间复杂度为 <span class="arithmatex">\(O(n^2)\)</span> ,内存占用较多。</p>
|
||||
<h3 id="_2">邻接表<a class="headerlink" href="#_2" title="Permanent link">¶</a></h3>
|
||||
<p>「邻接表 Adjacency List」使用 <span class="arithmatex">\(n\)</span> 个链表来表示图,链表结点表示顶点。第 <span class="arithmatex">\(i\)</span> 条链表对应顶点 <span class="arithmatex">\(i\)</span> ,其中存储了该顶点的所有邻接顶点(即与该顶点相连的顶点)。</p>
|
||||
<p>「邻接表 Adjacency List」使用 <span class="arithmatex">\(n\)</span> 个链表来表示图,链表节点表示顶点。第 <span class="arithmatex">\(i\)</span> 条链表对应顶点 <span class="arithmatex">\(i\)</span> ,其中存储了该顶点的所有邻接顶点(即与该顶点相连的顶点)。</p>
|
||||
<p><img alt="图的邻接表表示" src="../graph.assets/adjacency_list.png" /></p>
|
||||
<p align="center"> Fig. 图的邻接表表示 </p>
|
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|
||||
<ul>
|
||||
<li><strong>添加边</strong>:在顶点对应链表的末尾添加边即可,使用 <span class="arithmatex">\(O(1)\)</span> 时间。因为是无向图,所以需要同时添加两个方向的边。</li>
|
||||
<li><strong>删除边</strong>:在顶点对应链表中查找并删除指定边,使用 <span class="arithmatex">\(O(m)\)</span> 时间。在无向图中,需要同时删除两个方向的边。</li>
|
||||
<li><strong>添加顶点</strong>:在邻接表中添加一个链表,并将新增顶点作为链表头结点,使用 <span class="arithmatex">\(O(1)\)</span> 时间。</li>
|
||||
<li><strong>添加顶点</strong>:在邻接表中添加一个链表,并将新增顶点作为链表头节点,使用 <span class="arithmatex">\(O(1)\)</span> 时间。</li>
|
||||
<li><strong>删除顶点</strong>:需遍历整个邻接表,删除包含指定顶点的所有边,使用 <span class="arithmatex">\(O(1)\)</span> 时间。</li>
|
||||
<li><strong>初始化</strong>:在邻接表中创建 <span class="arithmatex">\(n\)</span> 个顶点和 <span class="arithmatex">\(2m\)</span> 条边,使用 <span class="arithmatex">\(O(n + m)\)</span> 时间。</li>
|
||||
</ul>
|
||||
@@ -2537,7 +2537,7 @@
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<p>以下是基于邻接表实现图的代码示例。细心的同学可能注意到,<strong>我们在邻接表中使用 <code>Vertex</code> 结点类来表示顶点</strong>,这样做的原因有:</p>
|
||||
<p>以下是基于邻接表实现图的代码示例。细心的同学可能注意到,<strong>我们在邻接表中使用 <code>Vertex</code> 节点类来表示顶点</strong>,这样做的原因有:</p>
|
||||
<ul>
|
||||
<li>如果我们选择通过顶点值来区分不同顶点,那么值重复的顶点将无法被区分。</li>
|
||||
<li>如果类似邻接矩阵那样,使用顶点列表索引来区分不同顶点。那么,假设我们想要删除索引为 <span class="arithmatex">\(i\)</span> 的顶点,则需要遍历整个邻接表,将其中 <span class="arithmatex">\(> i\)</span> 的索引全部减 <span class="arithmatex">\(1\)</span>,这样操作效率较低。</li>
|
||||
@@ -2625,7 +2625,7 @@
|
||||
<a id="__codelineno-11-4" name="__codelineno-11-4" href="#__codelineno-11-4"></a><span class="w"> </span><span class="c1">// 邻接表,key: 顶点,value:该顶点的所有邻接顶点</span>
|
||||
<a id="__codelineno-11-5" name="__codelineno-11-5" href="#__codelineno-11-5"></a><span class="w"> </span><span class="n">unordered_map</span><span class="o"><</span><span class="n">Vertex</span><span class="o">*</span><span class="p">,</span><span class="w"> </span><span class="n">vector</span><span class="o"><</span><span class="n">Vertex</span><span class="o">*>></span><span class="w"> </span><span class="n">adjList</span><span class="p">;</span>
|
||||
<a id="__codelineno-11-6" name="__codelineno-11-6" href="#__codelineno-11-6"></a>
|
||||
<a id="__codelineno-11-7" name="__codelineno-11-7" href="#__codelineno-11-7"></a><span class="w"> </span><span class="cm">/* 在 vector 中删除指定结点 */</span>
|
||||
<a id="__codelineno-11-7" name="__codelineno-11-7" href="#__codelineno-11-7"></a><span class="w"> </span><span class="cm">/* 在 vector 中删除指定节点 */</span>
|
||||
<a id="__codelineno-11-8" name="__codelineno-11-8" href="#__codelineno-11-8"></a><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">remove</span><span class="p">(</span><span class="n">vector</span><span class="o"><</span><span class="n">Vertex</span><span class="o">*></span><span class="w"> </span><span class="o">&</span><span class="n">vec</span><span class="p">,</span><span class="w"> </span><span class="n">Vertex</span><span class="w"> </span><span class="o">*</span><span class="n">vet</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
|
||||
<a id="__codelineno-11-9" name="__codelineno-11-9" href="#__codelineno-11-9"></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">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">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">vec</span><span class="p">.</span><span class="n">size</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-11-10" name="__codelineno-11-10" href="#__codelineno-11-10"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">vec</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">vet</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
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||||
<li>在循环的每轮迭代中,弹出队首顶点并记录访问,然后将该顶点的所有邻接顶点加入到队列尾部;</li>
|
||||
<li>循环步骤 <code>2.</code> ,直到所有顶点被访问完成后结束;</li>
|
||||
</ol>
|
||||
<p>为了防止重复遍历顶点,我们需要借助一个哈希表 <code>visited</code> 来记录哪些结点已被访问。</p>
|
||||
<p>为了防止重复遍历顶点,我们需要借助一个哈希表 <code>visited</code> 来记录哪些节点已被访问。</p>
|
||||
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<div class="tabbed-content">
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<div class="tabbed-block">
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