Roman to Integer Explained

Problem Statement

Given a Roman numeral string s, convert it to an integer. Roman numerals use symbols I (1), V (5), X (10), L (50), C (100), D (500), and M (1000), with subtraction rules for cases like IV (4) and IX (9). This problem tests your ability to parse strings and handle special cases in numeral systems.

Example

Input: s = "MCMXCIV"

Output: 1994

Explanation: M = 1000, CM = 900, XC = 90, IV = 4, so 1000 + 900 + 90 + 4 = 1994.

Code

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

    public static void main(String[] args) {
        Solution sol = new Solution();
        System.out.println(sol.romanToInt("MCMXCIV")); // 1994
    }
}
            

def roman_to_int(s):
    roman = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    result = 0
    for i in range(len(s)):
        if i < len(s) - 1 and roman[s[i]] < roman[s[i + 1]]:
            result -= roman[s[i]]
        else:
            result += roman[s[i]]
    return result

# Example usage
print(roman_to_int("MCMXCIV"))  # 1994
            

function romanToInt(s) {
    const roman = { 'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000 };
    let result = 0;
    for (let i = 0; i < s.length; i++) {
        if (i < s.length - 1 && roman[s[i]] < roman[s[i + 1]]) {
            result -= roman[s[i]];
        } else {
            result += roman[s[i]];
        }
    }
    return result;
}

// Example usage
console.log(romanToInt("MCMXCIV")); // 1994
            

Explanation

• Create a mapping of Roman symbols to their integer values.
• Iterate through the string from left to right.
• If the current symbol’s value is less than the next, subtract it (e.g., IV = -1 + 5).
• Otherwise, add its value to the result.
• Return the final sum.

Note