Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 7

Description

Integer to English Words

Convert a non-negative integer num to its English words representation.

Example 1:

Input: num = 123
Output: "One Hundred Twenty Three"

Example 2:

Input: num = 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

Input: num = 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Constraints:

• 0 <= num <= 231 - 1

Solution

class Solution {
  const string ZERO = "Zero";
  const vector<pair<int, string>> units = {
    { 1000000000, "Billion" },
    { 1000000, "Million" },
    { 1000, "Thousand" },
    { 1, "" }
  };
  vector<string> ge20 = {
    "", // 0
    "", // 10
    "Twenty",
    "Thirty",
    "Forty",
    "Fifty",
    "Sixty",
    "Seventy",
    "Eighty",
    "Ninety" 
  };
  vector<string> lt20 = {
    "",
    "One",
    "Two",
    "Three",
    "Four",
    "Five",
    "Six",
    "Seven",
    "Eight",
    "Nine",
    "Ten",
    "Eleven",
    "Twelve",
    "Thirteen",
    "Fourteen",
    "Fifteen",
    "Sixteen",
    "Seventeen",
    "Eighteen",
    "Nineteen",
  };

  string numberLT1000ToWords(int num)  {
    string result;
    if (num >= 100)  {
      result += lt20[num / 100] + " Hundred";
      if (num % 100 == 0) return result;
      result += " ";
      num %= 100;
    }
        if (!num) return result;
    if (num < 20) {
      result += lt20[num];
    } else {
      result += ge20[num/10];
      if (num % 10)  result += " " + lt20[num % 10];
    }

    return result;
  }

  void numberPartToWords(string &result, int &num, const int threshold, const string &unit)  {
    if (num >= threshold)  {
      if (result.length()) result += " ";
      result += numberLT1000ToWords(num / threshold);
      if (unit.length()) result += " " + unit;
      num %= threshold;
    }
  }

  public:
    string numberToWords(int num)  {
      if (!num) return move(ZERO);
      string answer = "";
      for (const auto &[threshold, unit]: units) {
        numberPartToWords(answer, num, threshold, unit);
      }

      return answer;
    }
};