LeetCode 12-13:Integer to　Roman&&Roman to Integer

public class Solution {
    public String intToRoman(int num) {
        String[][] r = {  
            {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"},  
            {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"},  
            {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"},  
            {"", "M", "MM", "MMM"}  
        };  
          
        String ans = "";  
        int i = 0;  
        while (num > 0) {  
            int j = num % 10;  
            ans = r[i][j] + ans;  
            i++;  
            num /= 10;  
        }  
          
        return ans;  
    }
}

public class Solution {
     int romanToInt(String s) {  
        int ans = change(s.charAt(0));  
        for (int i = 1; i < s.length(); i++) {  
            if (change(s.charAt(i-1)) < change(s.charAt(i)) ){  
                ans += change(s.charAt(i)) - 2 * change(s.charAt(i-1));  
            } else {  
                ans += change(s.charAt(i));  
            }  
        }  
        return ans;  
    }  
      
    int change(char ch) {  
        switch (ch) {  
            case ‘I‘: return 1;  
            case ‘V‘: return 5;  
            case ‘X‘: return 10;  
            case ‘L‘: return 50;  
            case ‘C‘: return 100;  
            case ‘D‘: return 500;  
            case ‘M‘: return 1000;  
        }  
        return 0;  
    }  
}