Roman to Integer

Given a roman numeral, convert it to an integer.

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

Solution:

public class Solution {
    public int romanToInt(String s) {
        Map<Character, Integer> roman = new HashMap<>();
        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 ans = 0;
        for(int i=0; i<s.length()-1; i++){
            if(roman.get(s.charAt(i))<roman.get(s.charAt(i+1))) ans -= roman.get(s.charAt(i));
            else ans += roman.get(s.charAt(i));
        }
        return ans + roman.get(s.charAt(s.length()-1));
    }
}