Roman to Integer.java

class Solution {
    public int romanToInt(String s) {
        HashMap<Character, Integer> roman = new HashMap<>();// hashmap :O
        roman.put('I', 1);
        roman.put('V', 5);
        roman.put('X', 10);
        roman.put('L', 50);
        roman.put('C', 100);
        roman.put('D', 500);
        roman.put('M', 1000);      
        int result = 0;       
        for(int i = 0;i<s.length();i++){
            if(i > 0&& roman.get(s.charAt(i)) > roman.get(s.charAt(i -1)))
            {
                result +=roman.get(s.charAt(i)) - 2*roman.get(s.charAt(i - 1));//basically we need to subract 2 times, one because we already added it and we need to undo. two is for actual subraction.
            }
            else
            {
                result += roman.get(s.charAt(i));
            }
        }
        return result;
    }
}