题解 | 数字发音

#include <string>
#include <vector>
class ToString {
    vector<string> below20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine",
                              "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen",
                              "Sixteen", "Seventeen", "Eighteen", "Nineteen"
                             };
    vector<string> tens = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    vector<string> thousands = {"", "Thousand", "Million", "Billion"};

//num <1000;
    string helper(int num) {
        if (num == 0) return "";
        string res;
        if (num >= 100) {
            res += below20[num / 100] + " Hundred";
            num %= 100;
        }
        if (num < 20) {
            if (!res.empty()) res += " ";
            res += below20[num];
            return res;
        }

        if (!res.empty()) res += " ";
        res += tens[num / 10];
        num %= 10;
        if (num) res += " " + below20[num];
        return res;


    }


  public:
    string toString(int x) {
        // write code here
        if (x == 0) return "Zero";
        string res;
        int i = 0;
        while (x > 0) {
            int cur = x % 1000;
            if (cur) {
                string part = helper(cur);
                if (!thousands[i].empty()) part += " "+ thousands[i] + ",";
                res = part + res;
            }
            x /= 1000;
            ++i;
        }
        while (!res.empty() && (res.back() == ' ' || res.back() == ',')) {
            res.pop_back();

        }
        return res;

    }
};