查找算法

<?php
 /**
 sequence search
 从第一个元素开始，依次同每个元素比较
 */
 function seq_search($arr,$n,$k){
     for($i=0;$i<$n;$i++){
         if($arr[$i]==$k){
             break;
         }
     }
     if($i<$n){
         return $i;
     }else{
         return -1;
     }
 }
 
 /**
 binary search 使用了递归
 */
 function binary_search_recursive($arr,$low,$high,$k){
     if($low<=$high){
         $mid=intval(($low+$high)/2);
         if($arr[$mid]==$k){
             return $mid;
         }else if($arr[$mid]<$k){
             return binary_search($arr,$mid+1,$high,$k);
         }else{
             return binary_search($arr,$low,$mid-1,$k);
         }
     }
     return -1;
 }
 
 /**
 binary search 未使用递归
 */
 function binary_search($arr,$low,$high,$val){
    $mid = floor(($low+$high)/2);
    while($val!=$arr[$mid]&&$low<$high){
        if($val<$arr[$mid]){
            $high = $mid-1;
        }
        if($val>$arr[$mid]){
            $low = $mid+1;
        }
        $mid = floor(($low+$high)/2);
    }
    return $val==$arr[$mid]?$mid:-1;
 }
 
 $arr = array(9,6,10,2,5,3,1,8);
 echo seq_search($arr,8,2);
 echo '<br/>';
 echo binary_search_recursive($arr,0,7,2);
 echo '<br/>';
 echo binary_search($arr,0,7,2);