leetcode -- Integer to Roman

Given an integer, convert it to a roman numeral.

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

public String intToRoman(int num) {
        // Start typing your Java solution below
        // DO NOT write main() function
        StringBuffer result = new StringBuffer();
        String[][] mapping = {
                {"", "M", "MM", "MMM", "", "", "", "", "", ""}, //0 – 3000
                {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"}, //100 – 900
                {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"}, //10 – 90
                {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"} //0 – 9    
        };
        int scale = 1000;
        int i = 0;
        while(num > 0){
            int digit = num / scale;
            result.append(mapping[i++][digit]);
            num = num % scale;
            scale /= 10;
        }
        return result.toString();
    }