13. Roman to Integer

13_roman_to_integer.go

func romanToInt(s string) int {
    sum := 0
    var prev string

    for i := len(s) - 1; i >= 0; i-- {
        c := string(s[i])
        switch c {
        case "I":
            if prev == "V" || prev == "X" {
                sum -= 1
            } else {
                sum += 1
            }
        case "V":
            sum += 5
        case "X":
            if prev == "L" || prev == "C" {
                sum -= 10
            } else {
                sum += 10
            }
        case "L":
            sum += 50
        case "C":
            if prev == "D" || prev == "M" {
                sum -= 100
            } else {
                sum += 100
            }
        case "D":
            sum += 500
        case "M":
            sum += 1000
        }

        prev = c
    }

    return sum
}