语音报数

题目描述
有一个非负整数，请编写一个算法，打印该整数的英文描述。
给定一个int x，请返回一个string，为该整数的英文描述。
测试样例：
1234
返回：”One Thousand,Two Hundred Thirty Four”

class ToString {
public:
    vector<string> digits = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine","Ten" };
    vector<string> teens = {"", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };
    vector<string> tens = {"","","Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };
    vector<string> bigs = { "Hundred", "Thousand", "Million","Billion"};
        string fayin(int x)
        {
            string res;
            if(x < 0)
                return res;
            if(x <= 10 && x >0)
                res = digits[x];
            else if(x < 20&& x > 10)
                res = teens[x-10];
            else if(x < 100&& x >=20)
                res = tens[x/10]+ (x % 10 > 0 ? " " : "") +fayin(x%10);
            else if(x < 1000 && x >=100)
                res = fayin(x/100) + " " +bigs[0] +  (x % 100 > 0 ? " " : "") +fayin(x%100);
            else if(x < 1000000 && x >=1000)
                res = fayin(x/1000) + " " +bigs[1] +  (x % 1000 > 0 ? "," : "") + fayin(x%1000);
            else if(x < 1000000000 && x >= 1000000)
                res = fayin(x/1000000) + " " +bigs[2] + (x % 1000000 > 0 ? "," : "") + fayin(x%1000000);
            else if(x < 1000000000000 && x >= 1000000000)
                res = fayin(x/1000000000) + " " +bigs[3] + (x % 1000000000 > 0 ? "," : "") + fayin(x%1000000000);

            return res;

        }
    string toString(int x) {
        // write code here
        string res;
        if(x < 0)
            return res;
        else if(x == 0)
            res = "zero";
        else
        res = fayin(x);
        return res;
    }
};