<?php
#二分查找
function binarySearch(Array $arr, $target) {
$low = 0;
$high = count($arr) - 1;

    while($low <= $high) {
        $mid = floor(($low + $high) / 2);
        #找到元素
        if($arr[$mid] == $target) return $mid;
        #中元素比目标大,查找左部
        if($arr[$mid] > $target) $high = $mid - 1;
        #重元素比目标小,查找右部
        if($arr[$mid] < $target) $low = $mid + 1;
    }
    
    #查找失败
    return false;
}

$arr = array(1, 3, 5, 7, 9, 11);
$inx = binarySearch($arr, 1);
var_dump($inx);

?>