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){
        String[][]  arr={{"","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"}};
        StringBuilder roman = new StringBuilder();
        roman.append(arr[3][num/1000%10]);
        roman.append(arr[2][num/100%10]);
        roman.append(arr[1][num/10%10]);
        roman.append(arr[0][num%10]);
        return roman.toString();
    }