8.5.3 字符串面試題3

四、寫一個函數，算出兩個文件的相對路徑
如：
$a=’/a/b/c/d/e.php’
$b=’/a/b/12/34/c.php’
計算出$b相對于$a的相對路徑應該是../../c/d

test.php

<?php
    function abspath($a, $b) {
        //第一步去除公共的目錄結構
        //  $a = "/a/b/c/d/e.php";
        //  $b = "/a/b/12/34/c.php";
        $a = dirname($a);    //  /a/b/c/d
        $b = dirname($b);    //  /a/b/12/34
        $a = trim($a, "/");   //   a/b/c/d
        $b = trim($b, "/");   //   a/b/12/34
        $a = explode("/", $a);  //  array("a", "b", "c", "d")
        $b = explode("/", $b);  //  array("a", "b", "12", "34")
        // $a = explode("/", trim(dirname($a), "/"));
        $num = max(count($a), count($b));
        for($i=0; $i<$num; $i++) {
            if($a[$i]==$b[$i]) {
                unset($a[$i]);
                unset($b[$i]);
            }else{
                break;
            }
        }
        //$a = array("c", "d");
        //$b = array("12", "34");
        //第二步：回到同級目錄， 進入另一個目錄
         $path = str_repeat("../", count($b)).implode("/", $a);    //  ../../c/d
        return $path;
    }
    $a = "/a/b/c/d/e/w/f/e.php";
    $b = "/a/b/12/34/100/c.php";
    // ../../c/d
    echo abspath($a, $b);