Roman To Integer

class Solution {
    public int romanToInt(String s) {
        int ans =0, num =0, next=0;

        for(int i = s.length() -1; i >= 0; i--){
            switch(s.charAt(i)){
                case 'M': num =1000;
                break;
                case 'D': num = 500;
                break;
                case 'C': num = 100;
                break;
                case 'L': num = 50;
                break;
                case 'X': num = 10;
                break;
                case 'V': num = 5;
                break;
                case 'I': num = 1;
                break;
            }

            if(num < next){
                ans -= num;
            }else{
                ans += num;
            }
            next = num;
        }
        return ans;
    }
}