php常见算法

• 2分查找
• 快速排序
• 选择排序
• 归并排序

1，二分查找做多需要log2n步；--对数是幂运算的逆运算。

<?php
ini_set('error_reporting', E_ALL);
ini_set('display_errors', 'on');
 function binary_search($a ,$b = 0) {

    $low = 0;
    $hign = count($a) -1;
    while ($hign >= $low) {
        $mid = floor(($low + $hign)/2);
        if ($a[$mid] == $b) {
            return $a[$mid];
        } elseif ($a[$mid] > $b) {
            $hign = $mid - 1;
        } elseif($a[$mid] < $b) {
            $low = $mid + 1;
        }
    }
    return '没有相关字符';
 }
$a = [1,2,33,47,555,666,888];
$b =34;
echo binary_search($a,$b);

<?php
//快速排序
$arr = [5,8,324,54,56,1,2,3];

function quick_sort($arr){
    $len = count($arr);
    if ($len <= 1) return $arr;
    $r = $l = [];
    for($i = 1;$i<$len ;$i++){
        
        if($arr[$i] > $arr[0]){
            $r[] = $arr[$i];
        } else {
            $l[] = $arr[$i];
        }
    }
        $r = quick_sort($r);
        $l = quick_sort($l);
    
    return array_merge($l , [$arr[0]], $r);
    
}
print_r(quick_sort($arr));

选择排序
<?php
$arr = [5,8,324,54,56,1,2,3];
$len = count($arr);

for($i=0 ;$i<$len ;$i++){
    $min = $i;
    for($j = $i+1;$j<$len ;$j++){
        if($arr[$j] < $arr[$min]){
            $min = $j;
        }
    }

    if ($min != $i){
        $tem = $arr[$i];
        $arr[$i] = $arr[$min];
        $arr[$min] = $tem;
    }
}
print_r($arr);

<?php
//归并排序
$arr = [5,8,324,54,56,1,2,3];

function m_sort($arr){
    $len = count($arr);
    if ($len <= 1) return $arr;
    
    $mid = floor($len/2);
    $left = array_slice($arr , 0 , $mid);
    $right = array_slice($arr,$mid);
    
    $left = m_sort($left);
    $right = m_sort($right);
    
    $m = [];
    while(count($left)>0 && count($right) >0){
        $m[] = $left[0] < $right[0] ? array_shift($left) : array_shift($right);
    }
    return array_merge($m, $left, $right);
    
}
print_r(m_sort($arr));