求相对路径的函数

<?php
$a = '/a/b/12/34/e.php';
$b = '/a/b/12/44/c.php';
function getRelativePath($a, $b) {
    $returnPath = array(dirname($b));
    $arrA = explode('/', $a);
    $arrB = explode('/', $returnPath[0]);
    for ($n = 1, $len = count($arrB); $n < $len; $n++) {
        if ($arrA[$n] != $arrB[$n]) {
            break;
        } 
    }
    if ($len - $n > 0) {
        $returnPath = array_merge($returnPath, array_fill(1, $len - $n, '..'));
    }
    
    $returnPath = array_merge($returnPath, array_slice($arrA, $n));
    return implode('/', $returnPath);
}
echo getRelativePath($a, $b);