php - 一维数组 转 多维数组问题，乱了！

Question

$arr = array('a','b','c','d');

转为

$brr = array(

'a'=>array(
    'b'=>array(
        'c'=>array(
            'd'=>array()
        )
    )
)

);

Answer 1

<?php
$arr = ['a', 'b', 'c', 'd'];
$child = array();
$res = [];
while($v = array_pop($arr)) {
    $res = [$v => $child];
    $child = $res;
}
print_r($res);

结果为

Array
(
    [a] => Array
        (
            [b] => Array
                (
                    [c] => Array
                        (
                            [d] => Array
                                (
                                )
                        )
                )
        )
)

Answer 2

看到结构想到了递归，具体代码如下：

    function toMany ($arr) {
        $res = array();
        burnArr($res, $arr);
        return $res;
    }
    
    function burnArr (&$arr, $keys) {
        if ( !empty($keys) ) {
            $val = array_shift($keys);
            $arr[$val] = array();
            burnArr($arr[$val], $keys);
        } else {
            return ;
        }
    }