check whether an array can be turn to non-descending order by a single swap 2 elements

non-descending-order.php

<?php

/**
 * check whether an array can be turn to non-descending order by a single swap 2 elements
 *
 * @param array $a
 * @return bool
 * @author Phan Vu Hoang <vu-hoang.phan@ekino.com>
 */
function solution($a)
{
    $a1 = $a;
    asort($a);
    $flag = true;
    foreach ($a as $key => $value) {
        if ($value != $a1[$key]) {
            $flag = false;
        }
    }
    if ($flag) {
        return true;
    } else {
        $result = array_diff_assoc($a1, $a);
        return (count($result) == 2) ? true : false;
    }

}