PHP：多维数组扁平化

<?php$arr= [
    [
'1', '2'    ],
    [
'1', '4', '5'    ],
];
functionflatten($arr)
{
$result= [];
foreach ($arras$k=>$v) {
if (is_array($v)) {
$result=array_merge($result, flatten($v));
        } else {
$result[] =$v;
        }
    }
return$result;
}
print_r(json_encode(flatten($arr)));
// ["1","2","1","4","5"]// 去重处理，注意需要取值操作print_r(json_encode(array_values(array_unique(flatten($arr)))));
// ["1","2","4","5"]