Detailed explanation of common PHP algorithms or functions

<?php

//不用第三个变量，交换两个变量的值
function changeVar()
{
    $a = &#39;123&#39;;
    $b = &#39;456&#39;;
    
    list($a, $b) = array($b, $a);
    
    echo $a . &#39;-&#39; . $b;
}
//文件锁
function fileLock()
{
    $fp = fopen(&#39;./tmp.txt&#39;, &#39;w+&#39;);
    if (flock($fp, LOCK_EX)) { //独占锁定
        fwrite($fp, &#39;write something\n&#39;);
        flock($fp, LOCK_UN);//释放锁
    } else {
        echo "can&#39;t lock!";
    }
    fclose($fp);
}

//获取文件后缀
function getExtName($url)
{
    $path_info = pathinfo($url);
    $ext_name = $path_info[&#39;extension&#39;];
    echo $ext_name;
}

/*斐波那契数列第n位是什么，递归实现
* @param int $n 位数
*/
function fibonacci($n)
{
    $return = 1;
    if ($n <= 0) {
        $return = 0;
    } elseif ($n <= 2) {
        $return = 1;
    } else {
        $return = fibonacci($n - 2) + fibonacci($n - 1);
    }

    return $return;
}

//自己实现number_format
function numFormat($num)
{
    // return number_format($num);
    $num = strrev($num);//反转
    $num = str_split($num, 3);//分割成数组
    $num = implode(&#39;,&#39;, $num);//拼接
    $num = strrev($num);//再反转
    return $num;
}

//冒泡排序
function bubble_sort(&$arr)
{
    $len = count($arr);
    for ($i = 0; $i < $len; $i++) {
        for ($j = 1; $j < $len - $i; $j++) {
            if ($arr[$j - 1] > $arr[$j]) {
                $tmp = $arr[$j];
                $arr[$j] = $arr[$j - 1];
                $arr[$j - 1] = $tmp;
            }
        }
    }
}

//快速排序
function quickSort($arr)
{
    $len = count($arr);
    if ($len <= 1) {
        return $arr;
    }

    $base = $arr[0];
    $left_array = array();
    $right_array = array();
    for ($i = 1; $i < $len; $i++) {
        if ($arr[$i] > $base) {
            $left_array[] = $arr[$i];
        } else {
            $right_array[] = $arr[$i];
        }
    }
    $left_array = quickSort($left_array);
    $right_array = quickSort($right_array);
    return $left_array;
}

//二维数组排序
function array_sort($arr, $keys, $order = &#39;ASC&#39;)
{
    if (!is_array($arr)) {
        return false;
    }
    $keysvalue = array();
    foreach ($arr as $k => $v) {
        $keysvalue[$k] = $v[$keys];
    }

    if ($order == &#39;ASC&#39;) {
        asort($keysvalue);
    } else {
        arsort($keysvalue);
    }
    reset($keysvalue);
    foreach ($keysvalue as $k => $v) {
        $keysort[$k] = $k;
    }
    foreach ($keysort as $k => $v) {
        $new_arr[] = $arr[$v];
    }
    
    return $new_arr;
}
//使用自带函数二维数组排序
function array_sort2(&$arr, $keys, $order = SORT_ASC)
{
    array_multisort(array_column($arr, $keys), $order, $arr);
}

//二分查找
function bin_sch($arr, $low, $top, $target)
{
    sort($arr);
    while ($low <= $top) {
        $mid = floor(($low + $top)/2);
        if ($arr[$mid] == $target) {
            return $arr[$mid];
        } elseif ($arr[$mid] < $target) {
            $low = $mid + 1;
            bin_sch($arr, $low, $top, $target);
        } else {
            $top = $mid - 1;
            bin_sch($arr, $low, $top, $target);
        }
    }
    return -1;
}

//遍历文件夹
function my_scandir($dir)
{
    $files = array();
    if ($handle = opendir($dir)) {
        while (($filename = readdir($handle)) !== false) {
            if ($filename != &#39;.&#39; && $filename != &#39;..&#39;) {
                if (is_dir($dir."/".$filename)) {
                    $files[$filename] = my_scandir($dir."/".$filename);
                } else {
                    $files[] = $filename;
                }
            }
        } 
        closedir($handle);
        return $files;
    }
}

//get_user_id改为getUserId
function change($str)
{
    $str = ucwords($str, &#39;_&#39;);
    return str_replace(&#39;_&#39;, &#39;&#39;, $str);
}

//反转每个单词
function convert($input) {
    $arr = explode(" ", $input);
    array_walk($arr, function (&$value) {
        $value = strrev($value);
    });
    $output =  implode(" ", $arr);
    echo $output;
}