算法-随手写的二分查找

<?php
    function search($arr, $num) {
        $len = count($arr);
        
        $start = 0;
        $end = $len - 1;
        $mid = floor(($start + $end) / 2);
        
        while($start <= $end) {
            echo $start, ':', $mid, ':', $end, '<br />'; //输出查找流程
            
            if ($num == $arr[$mid]) {
                return $mid;
            }elseif ($num > $arr[$mid]) {
                $start = $mid + 1;
            } elseif ($num < $arr[$mid]) {
                $end = $mid - 1;
            }
            $mid = floor(($start + $end) / 2);
        }
        return -1;
    }
    
    $search_arr = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
    echo '4的索引值为:', search($search_arr, 4);