private String toString(int number){
        
        switch(number){
            case 0:
                return " Zero";
            case 1:
                return " One";
            case 2:
                return " Two";
            case 3:
                return " Three";
            case 4:
                return " Four";
            case 5:
                return " Five";
            case 6:
                return " Six";
            case 7:
                return " Seven";
            case 8:
                return " Eight";
            case 9:
                return " Nine";
            case 10:
                return " Ten";
            case 11:
                return " Eleven";
            case 12:
                return " Twelve";
            case 13:
                return " Thrirteen";
            case 14:
                return " Fourteen";
            case 15:
                return " Fifteen";
            case 16:
                return " Sixteen";
            case 17:
                return " Seventeen";
            case 18:
                return " Eighteen";
            case 19:
                return " Nineteen";
            case 20:
                return " Twenty";
            case 30:
                return " Thirty";
            case 40:
                return " Forty";
            case 50:
                return " Fifty";
            case 60:
                return " Sixty";
            case 70:
                return " Seventy";
            case 80:
                return " Eighty";
            case 90:
                return " Ninety";
            case 100:
                return " Hundred";
            case 1000:
                return " Thousand";
            case 1000000:
                return " Million";
            case 1000000000:
                return " Billion";
            default:
                throw new IllegalArgumentException();
            }
    }
Convert a number into words

Reference
https://leetcode.com/problems/integer-to-english-words/
src/com/interview/misc/NumberToWord.java