Problem
Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.
Example,
123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"Solution
class Solution { private String[] belowTen = new String[] {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"}; private String[] tenToTwenty = new String[] {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"}; private String[] tens = new String[] {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"}; public String numberToWords(int num) { if (num == 0) return "Zero"; return helper(num); } private String helper(int num) { String result; if (num < 10) result = belowTen[num]; else if (num < 20) result = tenToTwenty[num-10]; else if (num < 100) result = tens[num/10] + " " + belowTen[num%10]; else if (num < 1000) result = belowTen[num/100] + " Hundred " + helper(num%100); else if (num < 10000) result = belowTen[num/1000] + " Thousand " + helper(num%1000); else if (num < 1000000) result = helper(num/1000) + " Thousand " + helper(num%1000); else if (num < 1000000000) result = helper(num/1000000) + " Million " + helper(num%1000000); else result = helper(num/1000000000) + " Billion " + helper(num%1000000000); return result.trim(); }}