LeetCode-Solutions-in-Cpp17

Solutions to high-frequency interview questions of LeetCode in C++17, taking into account both efficiency and comprehensibility.

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class Solution {
 public:
  string numberToWords(int num) {
    if (!num) {
      return "Zero";
    }
    string res;
    for (int i = 1000000000, j = 0; i > 0; i /= 1000, ++j) {
      if (num >= i) {
        res += getPart(num / i) + big[j] + ' ';
        num %= i;
      }
    }
    while (res.back() == ' ') {
      res.pop_back();
    }
    return res;
  }

  string getPart(int num) {
    string res;
    if (num >= 100) {
      res += small[num / 100] + " Hundred ";
      num %= 100;
    }
    if (!num) {
      return res;
    }
    if (num >= 20) {
      res += decade[num / 10] + ' ';
      num %= 10;
    }
    if (!num) {
      return res;
    }
    res += small[num] + ' ';
    return res;
  }

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