/*
 * @lc app=leetcode id=13 lang=java
 *
 * [13] Roman to Integer
 */

// @lc code=start

import java.util.Arrays;

class Solution {
    public int romanToInt(String s) {
        return romanToInt(0, s, 0);
    }

    private int romanToInt(int c, String s, int i) {
        if(i == s.length()) {
            return c;
        }
        int r;
        if(i+1 < s.length() && COMBINED_FORMAT_LIST.contains(s.substring(i, i+2))) {
            r = romanToInt(c+getValue(s.substring(i, i+2)), s, i+2);
        } else {
            r = romanToInt(c+getValue(s.substring(i, i+1)), s, i+1);
        }
        return r;
    }

    private int getValue(String s) {
        int r = 0;
        switch(s) {
            case "IV":
                r = 4;
                break;
            case "IX":
                r = 9;
                break;
            case "XL":
                r = 40;
                break;
            case "XC":
                r = 90;
                break;
            case "CD":
                r = 400;
                break;
            case "CM":
                r = 900;
                break;
            case "I":
                r = 1;
                break;
            case "V":
                r = 5;
                break;
            case "X":
                r = 10;
                break;
            case "L":
                r = 50;
                break;
            case "C":
                r = 100;
                break;
            case "D":
                r = 500;
                break;
            case "M":
                r = 1000;
                break;
            default: 
                throw new RuntimeException("invalid expr: "+s);
        }
        return r;
    }

    public static final List<String> COMBINED_FORMAT_LIST = Arrays.asList(
        "IV","IX", "XL", "XC", "CD", "CM"
    );
}
// @lc code=end