LeetCode Solutions

			

class Solution {
 public:
  string numberToWords(int num) {
    if (num == 0)
      return "Zero";
    return helper(num);
  }

 private:
  const vector<string> belowTwenty{
      "",        "One",     "Two",       "Three",    "Four",
      "Five",    "Six",     "Seven",     "Eight",    "Nine",
      "Ten",     "Eleven",  "Twelve",    "Thirteen", "Fourteen",
      "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
  const vector<string> tens{"",      "",      "Twenty",  "Thirty", "Forty",
                            "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

  string helper(int num) {
    string s;

    if (num < 20)
      s = belowTwenty.at(num);
    else if (num < 100)
      s = tens.at(num / 10) + " " + belowTwenty.at(num % 10);
    else if (num < 1000)
      s = helper(num / 100) + " Hundred " + helper(num % 100);
    else if (num < 1000000)
      s = helper(num / 1000) + " Thousand " + helper(num % 1000);
    else if (num < 1000000000)
      s = helper(num / 1000000) + " Million " + helper(num % 1000000);
    else
      s = helper(num / 1000000000) + " Billion " + helper(num % 1000000000);

    trim(s);
    return s;
  }

  void trim(string& s) {
    s.erase(0, s.find_first_not_of(' '));
    s.erase(s.find_last_not_of(' ') + 1);
  }
};

			

class Solution {
  public String numberToWords(int num) {
    return num == 0 ? "Zero" : helper(num);
  }

  private final String[] belowTwenty = {"",        "One",     "Two",       "Three",    "Four",
                                        "Five",    "Six",     "Seven",     "Eight",    "Nine",
                                        "Ten",     "Eleven",  "Twelve",    "Thirteen", "Fourteen",
                                        "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
  private final String[] tens = {"",      "",      "Twenty",  "Thirty", "Forty",
                                 "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

  private String helper(int num) {
    StringBuilder s = new StringBuilder();

    if (num < 20)
      s.append(belowTwenty[num]);
    else if (num < 100)
      s.append(tens[num / 10]).append(" ").append(belowTwenty[num % 10]);
    else if (num < 1000)
      s.append(helper(num / 100)).append(" Hundred ").append(helper(num % 100));
    else if (num < 1000000)
      s.append(helper(num / 1000)).append(" Thousand ").append(helper(num % 1000));
    else if (num < 1000000000)
      s.append(helper(num / 1000000)).append(" Million ").append(helper(num % 1000000));
    else
      s.append(helper(num / 1000000000)).append(" Billion ").append(helper(num % 1000000000));

    return s.toString().trim();
  }
}

			

class Solution:
  def numberToWords(self, num: int) -> str:
    if num == 0:
      return "Zero"

    belowTwenty = ["",        "One",       "Two",      "Three",
                   "Four",    "Five",      "Six",      "Seven",
                   "Eight",   "Nine",      "Ten",      "Eleven",
                   "Twelve",  "Thirteen",  "Fourteen", "Fifteen",
                   "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
    tens = ["",      "Ten",   "Twenty",  "Thirty", "Forty",
            "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]

    def helper(num: int) -> str:
      if num < 20:
        s = belowTwenty[num]
      elif num < 100:
        s = tens[num // 10] + " " + belowTwenty[num % 10]
      elif num < 1000:
        s = helper(num // 100) + " Hundred " + helper(num % 100)
      elif num < 1000000:
        s = helper(num // 1000) + " Thousand " + helper(num % 1000)
      elif num < 1000000000:
        s = helper(num // 1000000) + " Million " + \
            helper(num % 1000000)
      else:
        s = helper(num // 1000000000) + " Billion " + \
            helper(num % 1000000000)

      return s.strip()

    return helper(num)