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 class Solution {
    public String intToRoman(int num) {
        StringBuffer roman = new StringBuffer();
        int[] units = new int[]{1000,900,500,400,100,90,50,40,10,9,5,4,1};
        String[] romanNumeral = new String[]{"M","CM", "D", "CD", "C", "XC", "L",
        		"XL", "X", "IX", "V", "IV", "I"};
        int i = 0;
        while(num > 0){
        	if(num >= units[i]){
        		roman.append(romanNumeral[i]);
        		num -= units[i];
        	}
        	else
        		++i;
        }
        return roman.toString();    
    }
}