content: class Solution {
      public String numberToWords(int num) {
      if(num == 0)
          return "Zero";
      String[] bigString = new String[]{"Thousand","Million","Billion"};
      String result =  numberToWordsHelper(num%1000);
      num = num/1000;
      if(num > 0 && num%1000>0){
          result = numberToWordsHelper(num%1000) + "Thousand " + result;
      }
      num = num/1000;
      if(num > 0 && num%1000>0){
          result = numberToWordsHelper(num%1000) + "Million " + result;
      }
      num = num/1000;
      if(num > 0){
          result = numberToWordsHelper(num%1000) + "Billion " + result;
      }
      return result.trim();
  }
  
  public String numberToWordsHelper(int num){
      String[] digitString = new String[]{"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
      String[] teenString = new String[]{"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen","Eighteen", "Nineteen"};
      String[] tenString = new String[]{"","","Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
      String result = "";
      if(num > 99){
          result += digitString[num/100] + " Hundred ";
      }
      num = num % 100;
      if(num < 20 && num > 9){
          result += teenString[num%10]+" ";
      }else{
          if(num > 19){
              result += tenString[num/10]+" ";
          }
          num = num % 10;
          if(num > 0)
              result += digitString[num]+" ";
      }
      return result;
  }
  }
  