Simple integer to roman conversion in PHP

int_to_roman.php

<?php 

class Solution {

    /**
     * @param String $s
     * @return Integer
     */
    function romanToInt($s) {
        $map = [
            'I' => 1,
            'V' => 5,
            'X' => 10,
            'L' => 50,
            'C' => 100,
            'D' => 500,
            'M' => 1000
        ];
        $sum = 0;
        $last = 0;
        for ($i = strlen($s) - 1; $i >= 0; $i--) {
            $cur = $map[$s[$i]];
            if ($cur < $last) {
                $sum -= $cur;
            } else {
                $sum += $cur;
            }
            $last = $cur;
        }
        return $sum;
        
    }
}

?>