PHP-二分查找

function binarySearch($arr,$findval,$leftIndex,$rigthIndex){
    if($leftIndex > $rigthIndex){
       echo ‘找不到这个数‘;
       return ;
    }
    $middleIndex = round(($leftIndex+$rigthIndex)/2);
    if($findval > $arr[$middleIndex]){
        binarySearch($arr, $findval, $middleIndex+1, $rigthIndex);
    }else if($findval < $arr[$middleIndex]){
        binarySearch($arr, $findval, $leftIndex, $middleIndex-1);
    }else{
        echo ‘这个数的下标是‘. $middleIndex;
    }
}