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chapter_hashing/hash_algorithm/index.html
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</code></pre></div>
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<div class="highlight"><span class="filename">built_in_hash.rs</span><pre><span></span><code><a id="__codelineno-22-1" name="__codelineno-22-1" href="#__codelineno-22-1"></a>
<div class="highlight"><span class="filename">built_in_hash.rs</span><pre><span></span><code><a id="__codelineno-22-1" name="__codelineno-22-1" href="#__codelineno-22-1"></a><span class="k">use</span><span class="w"> </span><span class="n">std</span>::<span class="n">collections</span>::<span class="n">hash_map</span>::<span class="n">DefaultHasher</span><span class="p">;</span>
<a id="__codelineno-22-2" name="__codelineno-22-2" href="#__codelineno-22-2"></a><span class="k">use</span><span class="w"> </span><span class="n">std</span>::<span class="n">hash</span>::<span class="p">{</span><span class="n">Hash</span><span class="p">,</span><span class="w"> </span><span class="n">Hasher</span><span class="p">};</span>
<a id="__codelineno-22-3" name="__codelineno-22-3" href="#__codelineno-22-3"></a>
<a id="__codelineno-22-4" name="__codelineno-22-4" href="#__codelineno-22-4"></a><span class="kd">let</span><span class="w"> </span><span class="n">num</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span>
<a id="__codelineno-22-5" name="__codelineno-22-5" href="#__codelineno-22-5"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">num_hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-6" name="__codelineno-22-6" href="#__codelineno-22-6"></a><span class="n">num</span><span class="p">.</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">num_hasher</span><span class="p">);</span>
<a id="__codelineno-22-7" name="__codelineno-22-7" href="#__codelineno-22-7"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash_num</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">num_hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-8" name="__codelineno-22-8" href="#__codelineno-22-8"></a><span class="c1">// 整数 3 的哈希值为 568126464209439262</span>
<a id="__codelineno-22-9" name="__codelineno-22-9" href="#__codelineno-22-9"></a>
<a id="__codelineno-22-10" name="__codelineno-22-10" href="#__codelineno-22-10"></a><span class="kd">let</span><span class="w"> </span><span class="n">bol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kc">true</span><span class="p">;</span>
<a id="__codelineno-22-11" name="__codelineno-22-11" href="#__codelineno-22-11"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">bol_hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-12" name="__codelineno-22-12" href="#__codelineno-22-12"></a><span class="n">bol</span><span class="p">.</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">bol_hasher</span><span class="p">);</span>
<a id="__codelineno-22-13" name="__codelineno-22-13" href="#__codelineno-22-13"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash_bol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">bol_hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-14" name="__codelineno-22-14" href="#__codelineno-22-14"></a><span class="c1">// 布尔量 true 的哈希值为 4952851536318644461</span>
<a id="__codelineno-22-15" name="__codelineno-22-15" href="#__codelineno-22-15"></a>
<a id="__codelineno-22-16" name="__codelineno-22-16" href="#__codelineno-22-16"></a><span class="kd">let</span><span class="w"> </span><span class="n">dec</span>: <span class="kt">f32</span> <span class="o">=</span><span class="w"> </span><span class="mf">3.14159</span><span class="p">;</span>
<a id="__codelineno-22-17" name="__codelineno-22-17" href="#__codelineno-22-17"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">dec_hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-18" name="__codelineno-22-18" href="#__codelineno-22-18"></a><span class="n">dec</span><span class="p">.</span><span class="n">to_bits</span><span class="p">().</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">dec_hasher</span><span class="p">);</span>
<a id="__codelineno-22-19" name="__codelineno-22-19" href="#__codelineno-22-19"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash_dec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">dec_hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-20" name="__codelineno-22-20" href="#__codelineno-22-20"></a><span class="fm">println!</span><span class="p">(</span><span class="s">&quot;小数 {} 的哈希值为 {}&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">dec</span><span class="p">,</span><span class="w"> </span><span class="n">hash_dec</span><span class="p">);</span>
<a id="__codelineno-22-21" name="__codelineno-22-21" href="#__codelineno-22-21"></a><span class="c1">// 小数 3.14159 的哈希值为 2566941990314602357</span>
<a id="__codelineno-22-22" name="__codelineno-22-22" href="#__codelineno-22-22"></a>
<a id="__codelineno-22-23" name="__codelineno-22-23" href="#__codelineno-22-23"></a><span class="kd">let</span><span class="w"> </span><span class="kt">str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Hello 算法&quot;</span><span class="p">;</span>
<a id="__codelineno-22-24" name="__codelineno-22-24" href="#__codelineno-22-24"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">str_hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-25" name="__codelineno-22-25" href="#__codelineno-22-25"></a><span class="kt">str</span><span class="p">.</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">str_hasher</span><span class="p">);</span>
<a id="__codelineno-22-26" name="__codelineno-22-26" href="#__codelineno-22-26"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash_str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">str_hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-27" name="__codelineno-22-27" href="#__codelineno-22-27"></a><span class="c1">// 字符串 Hello 算法 的哈希值为 16092673739211250988</span>
<a id="__codelineno-22-28" name="__codelineno-22-28" href="#__codelineno-22-28"></a>
<a id="__codelineno-22-29" name="__codelineno-22-29" href="#__codelineno-22-29"></a><span class="kd">let</span><span class="w"> </span><span class="n">arr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="o">&amp;</span><span class="mi">12836</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="s">&quot;小哈&quot;</span><span class="p">);</span>
<a id="__codelineno-22-30" name="__codelineno-22-30" href="#__codelineno-22-30"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">tup_hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-31" name="__codelineno-22-31" href="#__codelineno-22-31"></a><span class="n">arr</span><span class="p">.</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">tup_hasher</span><span class="p">);</span>
<a id="__codelineno-22-32" name="__codelineno-22-32" href="#__codelineno-22-32"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash_tup</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">tup_hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-33" name="__codelineno-22-33" href="#__codelineno-22-33"></a><span class="c1">// 元组 (12836, &quot;小哈&quot;) 的哈希值为 1885128010422702749</span>
<a id="__codelineno-22-34" name="__codelineno-22-34" href="#__codelineno-22-34"></a>
<a id="__codelineno-22-35" name="__codelineno-22-35" href="#__codelineno-22-35"></a><span class="kd">let</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="n">new</span><span class="p">(</span><span class="mi">42</span><span class="p">);</span>
<a id="__codelineno-22-36" name="__codelineno-22-36" href="#__codelineno-22-36"></a><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">hasher</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">DefaultHasher</span>::<span class="n">new</span><span class="p">();</span>
<a id="__codelineno-22-37" name="__codelineno-22-37" href="#__codelineno-22-37"></a><span class="n">node</span><span class="p">.</span><span class="n">borrow</span><span class="p">().</span><span class="n">val</span><span class="p">.</span><span class="n">hash</span><span class="p">(</span><span class="o">&amp;</span><span class="k">mut</span><span class="w"> </span><span class="n">hasher</span><span class="p">);</span>
<a id="__codelineno-22-38" name="__codelineno-22-38" href="#__codelineno-22-38"></a><span class="kd">let</span><span class="w"> </span><span class="n">hash</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">hasher</span><span class="p">.</span><span class="n">finish</span><span class="p">();</span>
<a id="__codelineno-22-39" name="__codelineno-22-39" href="#__codelineno-22-39"></a><span class="c1">// 节点对象 RefCell { value: ListNode { val: 42, next: None } } 的哈希值为15387811073369036852</span>
</code></pre></div>
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chapter_hashing/hash_collision/index.html
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<p>为了解决该问题，我们可以采用「懒删除 lazy deletion」机制：它不直接从哈希表中移除元素，<strong>而是利用一个常量 <code>TOMBSTONE</code> 来标记这个桶</strong>。在该机制下，<span class="arithmatex">\(\text{None}\)</span> 和 <code>TOMBSTONE</code> 都代表空桶，都可以放置键值对。但不同的是，线性探测到 <code>TOMBSTONE</code> 时应该继续遍历，因为其之下可能还存在键值对。</p>
<p>然而，<strong>懒删除可能会加速哈希表的性能退化</strong>。这是因为每次删除操作都会产生一个删除标记，随着 <code>TOMBSTONE</code> 的增加，搜索时间也会增加，因为线性探测可能需要跳过多个 <code>TOMBSTONE</code> 才能找到目标元素。</p>
<p>为此，考虑在线性探测中记录遇到的首个 <code>TOMBSTONE</code> 的索引，并将搜索到的目标元素与该 <code>TOMBSTONE</code> 交换位置。这样做的好处是当每次查询或添加元素时，元素会被移动至距离理想位置（探测起始点）更近的桶，从而优化查询效率。</p>
<p>以下代码实现了一个包含懒删除的开放寻址（线性探测）哈希表。为了更加充分地使用哈希表的空间，我们将哈希表表看作是一个“环形数组”，当越过数组尾部时，回到头部继续遍历。</p>
<p>以下代码实现了一个包含懒删除的开放寻址（线性探测）哈希表。为了更加充分地使用哈希表的空间，我们将哈希表看作是一个“环形数组”，当越过数组尾部时，回到头部继续遍历。</p>
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chapter_hashing/hash_map/index.html
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</code></pre></div>
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<div class="highlight"><span class="filename">hash_map.go</span><pre><span></span><code><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a><span class="cm">/* 初始化哈希表 */</span>
<div class="highlight"><span class="filename">hash_map_test.go</span><pre><span></span><code><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a><span class="cm">/* 初始化哈希表 */</span>
<a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></a><span class="nx">hmap</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</span><span class="p">(</span><span class="kd">map</span><span class="p">[</span><span class="kt">int</span><span class="p">]</span><span class="kt">string</span><span class="p">)</span>
<a id="__codelineno-4-3" name="__codelineno-4-3" href="#__codelineno-4-3"></a>
<a id="__codelineno-4-4" name="__codelineno-4-4" href="#__codelineno-4-4"></a><span class="cm">/* 添加操作 */</span>