Skip to content
Related Articles

Related Articles

Improve Article
Convert a Roman Number to Decimal using Hashmap in Java
  • Last Updated : 27 Aug, 2020

Given a Roman numeral, the task is to find the corresponding decimal value.

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


Input: “III”

Output: 3

Input: “MDCCLX”

Output: 1760


  1. Loop through each character in the string containing the Roman numerals.
  2. Compare the value of the current roman symbol with the value of the roman symbol to its right. If the current value is greater than or equal to the value of the symbol to the right, add the current symbol’s value to the total. If the current value is smaller than the value of the symbol to the right, subtract the current symbol’s value from the total.

Below is the implementation of the above approach:


// Java Program to Convert a Roman
// Number to Decimal using Hashmap
import java.util.Scanner;
import java.util.HashMap;
class solution {
    int romanToInt(String s)
        // Create a empty hash map.
        HashMap<Character, Integer> map = new HashMap<>();
        // Putting value in hash map.
        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);
        // Creating integer variable to store result.
        int result = 0;
        // initialize loop to iterate in string.
        for (int i = 0; i < s.length(); i++) {
            // Checking that current element
            // is not smaller then previous
            if (i > 0
                && map.get(s.charAt(i))
                       > map.get(s.charAt(i - 1))) {
                result += map.get(s.charAt(i))
                          - 2 * map.get(s.charAt(i - 1));
            else {
                result += map.get(s.charAt(i));
        // Returning the integer value of Roman number.
        return result;
public class GFG {
    public static void main(String[] args)
        String s;
        // Scanner sc = new Scanner(;
        // s = sc.nextLine();
        solution gfg = new solution();



Attention reader! Don’t stop learning now. Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready. To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

My Personal Notes arrow_drop_up
Recommended Articles
Page :