Question

How to convert a Roman number to an integer in Java

Answer 1

import java.util.HashMap;
import java.util.Map;

public class RomanToInteger {
    private static final Map<Character, Integer> romanMap = new HashMap<>();

    static {
        romanMap.put('I', 1);
        romanMap.put('V', 5);
        romanMap.put('X', 10);
        romanMap.put('L', 50);
        romanMap.put('C', 100);
        romanMap.put('D', 500);
        romanMap.put('M', 1000);
    }

    public static int romanToInt(String s) {
        int total = 0;
        int prevValue = 0;

        for (int i = s.length() - 1; i >= 0; i--) {
            int currentValue = romanMap.get(s.charAt(i));
            if (currentValue < prevValue) {
                total -= currentValue;
            } else {
                total += currentValue;
            }
            prevValue = currentValue;
        }

        return total;
    }

    public static void main(String[] args) {
        String roman = "XCVII";
        
        int result = romanToInt(roman);
        
        System.out.println("The integer value of " + roman + " is " + result);
    }
}


/*
XCVII =
XC+V+I+I =
90+5+1+1 =
97
*/


/*
run:

The integer value of XCVII is 97

*/

 

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