PHP：array_flatten多维数组扁平化

/**
 * 多维数组扁平化
 * @param $array array
 * @return array
 */
if (!function_exists('array_flatten')) {
    function array_flatten($array)
    {
        $result = [];
        foreach ($array as $value) {
            if (is_array($value)) {
                $result = array_merge($result, array_flatten($value));
            } else {
                $result[] = $value;
            }
        }
        return $result;
    }
}

<?php
$arr = [
    [
        '1', '2'
    ],
    [
        '1', '4', '5'
    ],
];
print_r(json_encode(array_flatten($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(array_flatten($arr)))));
// ["1","2","4","5"]