In this post, we are going to solve the 13. Roman to Integer problem of Leetcode. This problem 13. Roman to Integer is a Leetcode easy level problem. Let’s see code, 13. Roman to Integer.

Problem

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I                      1
V                    5
X                    10
L                    50
C                  100
D                  500
M                 1000

For example, 2 is written as II in Roman numeral, just two one’s added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9.
• X can be placed before L (50) and C (100) to make 40 and 90.
• C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

Example 1 :

Input: s = "III"
Output: 3
Explanation: III = 3.

Example 2 :

Input: s = "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.

Example 3 :

Input: s = "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

Constraints

• 1 <= s.length <= 15
• s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
• It is guaranteed that s is a valid roman numeral in the range [1, 3999].

Now, let’s see the code of 13. Roman to Integer – Leetcode Solution.

Roman to Integer – Leetcode Solution

13. Roman to Integer – Solution in Java

class Solution {
    public static int romanToInt(String s) {
        if (s == null || s.length() == 0)
            return -1;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        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 len = s.length(), result = map.get(s.charAt(len - 1));
        for (int i = len - 2; i >= 0; i--) {
            if (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;
    }
}

13. Roman to Integer – Solution in C++

class Solution {
public:
    int romanToInt(string s) 
    {
        unordered_map<char, int> T = { { 'I' , 1 },
                                       { 'V' , 5 },
                                       { 'X' , 10 },
                                       { 'L' , 50 },
                                       { 'C' , 100 },
                                       { 'D' , 500 },
                                       { 'M' , 1000 } };

       int sum = T[s.back()];
       for (int i = s.length() - 2; i >= 0; --i) 
       {
           if (T[s[i]] < T[s[i + 1]])
           {
               sum -= T[s[i]];
           }
           else
           {
               sum += T[s[i]];
           }
       }

       return sum;
    }
};

13. Roman to Integer – Solution in Python

class Solution:
    def romanToInt(self, s: str) -> int:
        translations = {
            "I": 1,
            "V": 5,
            "X": 10,
            "L": 50,
            "C": 100,
            "D": 500,
            "M": 1000
        }
        number = 0
        s = s.replace("IV", "IIII").replace("IX", "VIIII")
        s = s.replace("XL", "XXXX").replace("XC", "LXXXX")
        s = s.replace("CD", "CCCC").replace("CM", "DCCCC")
        for char in s:
            number += translations[char]
        return number

Note: This problem 13. Roman to Integer is generated by Leetcode but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.