RomanToInteger.java

// Given a roman numeral, convert it to an integer.

// Input is guaranteed to be within the range from 1 to 3999

public class RomanToInteger {
    public int romanToInt(String s) {
        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 total = 0;

        for(int i = 0; i < s.length() - 1; i++) {
            if(map.get(s.charAt(i)) < map.get(s.charAt(i + 1))) {
                total -= map.get(s.charAt(i));
            } else {
                total += map.get(s.charAt(i));
            }
        }
        
        total += map.get(s.charAt(s.length() - 1));
        
        return total;
    }
}