IntegerToRoman.java

/**
 * 12. Integer to Roman
 * 
 * Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
 *  Symbol       Value
 *  I             1
 *  V             5
 *  X             10
 *  L             50
 *  C             100
 *  D             500
 *  M             1000
 * For example, 2 is written as II in Roman numeral, just two one's added together. 
 * 12 is written as XII, which is simply X + II. 
 * The number 27 is written as XXVII, which is XX + V + II.
 * Roman numerals are usually written largest to smallest from left to right.
 * However, the numeral for four is not IIII. 
 * Instead, the number four is written as IV. 
 * Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. 
 * There are six instances where subtraction is used:
 * I can be placed before V (5) and X (10) to make 4 and 9. 
 * X can be placed before L (50) and C (100) to make 40 and 90. 
 * C can be placed before D (500) and M (1000) to make 400 and 900.
 * Given an integer, convert it to a roman numeral.
 */

class IntegerToRoman {
    public String intToRoman(int theNum) {
        int[] values = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        String[] symbols = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
        StringBuilder sb = new StringBuilder();
        int index = 0;

        while (theNum > 0) {
            if (theNum >= values[index]) {
                sb.append(symbols[index]);
                theNum -= values[index];
            } else
                index++;
        }
        return sb.toString();
    }
}