PHP二分法查找之递归和迭代详解

程序员文章站 2022-04-03 13:38:54

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关于递归和迭代分别的时间复杂度，递归的时间复杂度是O(N)，而迭代的时间复杂度是O(logN),由y=N 和Y＝logN两条曲线我们知道，一定是O(logN)更优一些。本文主要和大家分享PHP二分法查找之递归和迭代详解，希望能帮助到大家。

以下是两段代码，和傻瓜式测效率的代码。

<?php  
  
function dichotomyIterationSearch($arr, $n, $v)  
{  
    $left   = 0;  
    $right  = $n - 1;  
    while ($left <= $right) {  
        $middle  = bcp(bcadd($right, $left), 2);  
        if ($arr[$middle] > $v) {  
            $right = $middle - 1;  
        } elseif ($arr[$middle] < $v) {  
            $left  = $middle + 1;  
        } else {  
            return $middle;  
        }  
    }  
    return -1;  
}  
  
  
$arr = [];  
for ($i=0;$i<300000;$i++){  
    $arr[] = $i;  
}  
list($first) = explode(" ",microtime());  
echo dichotomyIterationSearch($arr,count($arr),35387);echo '<br>';  
list($second) = explode(" ",microtime());  
echo round($second - $first,5)*1000000;  
  
  
function dichotomyRecursionSearch($arr, $low, $high, $v)  
{  
    $middle = bcp(bcadd($low, $high), 2);  
  
    if ($low < $high) {  
        if ($arr[$middle] > $v) {  
            $high = $middle - 1;  
            return dichotomyRecursionSearch($arr, $low, $high, $v);  
        } elseif ($arr[$middle] < $v) {  
            $low = $middle + 1;  
            return dichotomyRecursionSearch($arr, $low, $high, $v);  
        } else {  
            return $middle;  
        }  
    } elseif ($high == $low) {  
        if ($arr[$middle] == $v) {  
            return $middle;  
        } else {  
            return -1;  
        }  
    }  
    return -1;  
}  
  
  
$arr = [];  
for ($i=0;$i<300000;$i++){  
    $arr[] = $i;  
}  
echo "<br>";  
list($first) = explode(" ",microtime());  
echo dichotomyRecursionSearch($arr,0, count($arr),35387);echo '<br>';  
list($second) = explode(" ",microtime());  
echo round($second - $first, 5)*1000000;