13. Roman to Integer

class Solution {
    func romanToInt(_ s: String) -> Int {
        let roman: [Character : Int] = [
            "I" : 1,
            "V" : 5,
            "X" : 10,
            "L" : 50,
            "C" : 100,
            "D" : 500,
            "M" : 1000
        ]
        var old: Int = 0
        var result: Int = 0
        for character in s {
            let newInt = roman[character] ?? 0
            result += newInt > old ? newInt - old * 2  : newInt
            old = newInt
        }
        return result
    }
}