# 查找算法 二分查找 - 思路分析：數組中間的值floor((low+top)/2) - 先取數組中間的值floor((low+top)/2)然后通過與所需查找的數字進行比較， - 若比中間值大則將首值替換為中間位置下一個位置，繼續第一步的操作； - 若比中間值小，則將尾值替換為中間位置上一個位置，繼續第一步操作 - 重復第二步操作直至找出目標數字 ``` <pre class="calibre14">``` <span class="token5">function</span> <span class="token1">BinaryQuery</span><span class="token2">(</span>array $container<span class="token2">,</span> $search<span class="token2">)</span> <span class="token2">{</span> $top <span class="token">=</span> <span class="token1">count</span><span class="token2">(</span>$container<span class="token2">)</span><span class="token2">;</span> $low <span class="token">=</span> <span class="token3">0</span><span class="token2">;</span> <span class="token5">while</span> <span class="token2">(</span>$low <span class="token"><=</span> $top<span class="token2">)</span> <span class="token2">{</span> $mid <span class="token">=</span> <span class="token1">intval</span><span class="token2">(</span><span class="token1">floor</span><span class="token2">(</span><span class="token2">(</span>$low <span class="token">+</span> $top<span class="token2">)</span> <span class="token">/</span> <span class="token3">2</span><span class="token2">)</span><span class="token2">)</span><span class="token2">;</span> <span class="token5">if</span> <span class="token2">(</span><span class="token">!</span><span class="token1">isset</span><span class="token2">(</span>$container<span class="token2">[</span>$mid<span class="token2">]</span><span class="token2">)</span><span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> <span class="token4">'沒找著哦'</span><span class="token2">;</span> <span class="token2">}</span> <span class="token5">if</span> <span class="token2">(</span>$container<span class="token2">[</span>$mid<span class="token2">]</span> <span class="token">==</span> $search<span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> $mid<span class="token2">;</span> <span class="token2">}</span> $container<span class="token2">[</span>$mid<span class="token2">]</span> <span class="token"><</span> $search <span class="token">&&</span> $low <span class="token">=</span> $mid <span class="token">+</span> <span class="token3">1</span><span class="token2">;</span> $container<span class="token2">[</span>$mid<span class="token2">]</span> <span class="token">></span> $search <span class="token">&&</span> $top <span class="token">=</span> $mid <span class="token">-</span> <span class="token3">1</span><span class="token2">;</span> <span class="token2">}</span> <span class="token2">}</span> ``` ``` 遞歸版 二分查找 ``` <pre class="calibre16">``` <span class="token5">function</span> <span class="token1">BinaryQueryRecursive</span><span class="token2">(</span>array $container<span class="token2">,</span> $search<span class="token2">,</span> $low <span class="token">=</span> <span class="token3">0</span><span class="token2">,</span> $top <span class="token">=</span> <span class="token4">'default'</span><span class="token2">)</span> <span class="token2">{</span> $top <span class="token">==</span> <span class="token4">'default'</span> <span class="token">&&</span> $top <span class="token">=</span> <span class="token1">count</span><span class="token2">(</span>$container<span class="token2">)</span><span class="token2">;</span> <span class="token5">if</span> <span class="token2">(</span>$low <span class="token"><=</span> $top<span class="token2">)</span> <span class="token2">{</span> $mid <span class="token">=</span> <span class="token1">intval</span><span class="token2">(</span><span class="token1">floor</span><span class="token2">(</span>$low <span class="token">+</span> $top<span class="token2">)</span> <span class="token">/</span> <span class="token3">2</span><span class="token2">)</span><span class="token2">;</span> <span class="token5">if</span> <span class="token2">(</span><span class="token">!</span><span class="token1">isset</span><span class="token2">(</span>$container<span class="token2">[</span>$mid<span class="token2">]</span><span class="token2">)</span><span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> <span class="token4">'沒找著哦'</span><span class="token2">;</span> <span class="token2">}</span> <span class="token5">if</span> <span class="token2">(</span>$container<span class="token2">[</span>$mid<span class="token2">]</span> <span class="token">==</span> $search<span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> $mid<span class="token2">;</span> <span class="token2">}</span> <span class="token5">if</span> <span class="token2">(</span>$container<span class="token2">[</span>$mid<span class="token2">]</span> <span class="token"><</span> $search<span class="token2">)</span> <span class="token2">{</span> <span class="token5">return</span> <span class="token1">BinaryQueryRecursive</span><span class="token2">(</span>$container<span class="token2">,</span> $search<span class="token2">,</span> $mid <span class="token">+</span> <span class="token3">1</span><span class="token2">,</span> $top<span class="token2">)</span><span class="token2">;</span> <span class="token2">}</span> <span class="token5">else</span> <span class="token2">{</span> <span class="token5">return</span> <span class="token1">BinaryQueryRecursive</span><span class="token2">(</span>$container<span class="token2">,</span> $search<span class="token2">,</span> $low<span class="token2">,</span> $mid <span class="token">-</span> <span class="token3">1</span><span class="token2">)</span><span class="token2">;</span> <span class="token2">}</span> <span class="token2">}</span> <span class="token2">}</span> ``` ```