二分查找实现

binarySearch.php

<?php
/**
 * 二分查找
 * 
 * @param $a array
 * @param $v 查找的值
 * 
 * @return int 
 */
function binarySearch($a, $v)
{
    assert("is_array($a)");
    assert("is_string('$v')");
    
    sort($a);
    
    $left = 0;
    $right = count($a) - 1;
    
    while ($left <= $right) {
        $middle = $left + (($right - $left) >> 1);
        if ($a[$middle] > $v) {
            $right = $middle - 1;
        } elseif ($a[$middle] < $v) {
            $left = $middle + 1;
        } else {
            return $middle;
        }
    }
    
    return -1;
}