PHP 多维数组转换成一维

思路：递归思维

$arr = [[1,2,3,["active","hello"]],[7,[10,[21,"mmm"]]]];

function multi_to_one($arr){
	$res = array();
	foreach($arr as $v){
		if(!is_array($v)){
			array_push($res, $v);
		}else{
			$res = array_merge($res,multi_to_one($v));
		}
	}
	return $res;
}
print_r(multi_to_one($arr));

打印结果：

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => active
    [4] => hello
    [5] => 7
    [6] => 10
    [7] => 21
    [8] => mmm
)