Problem #13: Roman to Integer

Intuition & Strategy Breakdown

Iterate through the string from left to right. If a character's value is smaller than the next character's value, subtract it; otherwise, add it to the total sum.

Python Solution

class Solution:
    def romanToInt(self, s: str) -> int:
        roman = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
        res = 0
        for i in range(len(s)):
            if i + 1 < len(s) and roman[s[i]] < roman[s[i + 1]]:
                res -= roman[s[i]]
            else:
                res += roman[s[i]]
        return res

Java Solution

class Solution {
    public int romanToInt(String s) {
        Map roman = new HashMap<>();
        roman.put('I', 1); roman.put('V', 5); roman.put('X', 10);
        roman.put('L', 50); roman.put('C', 100); roman.put('D', 500); roman.put('M', 1000);
        int res = 0;
        for (int i = 0; i < s.length(); i++) {
            if (i + 1 < s.length() && roman.get(s.charAt(i)) < roman.get(s.charAt(i + 1))) {
                res -= roman.get(s.charAt(i));
            } else {
                res += roman.get(s.charAt(i));
            }
        }
        return res;
    }
}