273. 整数转换英文表示(模拟&递归)

Posted 2021-11-01 Harris-H

273. 整数转换英文表示 (模拟&递归)

用四个数组分别存：个位、11-19，20-90，(千、万，亿)

递归计算。

先计算有多少亿。

然后减去对应的亿部分。

再计算万部分，最后计算千部分。

$ep:1234567891$
$$\begin{gathered} 1234567891÷10^9=1\dots \dots 234567891(读一亿) \\ 234567891÷10^6=234\dots \dots 567891(读二千三百四十万) \\ 567891÷10^3=567\dots \dots 891(读五百六十七千) \\ 891÷1=891\dots \dots 0(读八百九十一) \end{gathered}$$
参考code

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

    string numberToWords(int num) {
        if (num == 0) {
            return "Zero";
        }
        string sb;
        for (int i = 3, unit = 1000000000; i >= 0; i--, unit /= 1000) {
            int curNum = num / unit;
            if (curNum != 0) {
                num -= curNum * unit;
                string curr;
                recursion(curr, curNum);
                curr = curr + thousands[i] + " ";
                sb = sb + curr;
            }
        }
        while (sb.back() == ' ') {
            sb.pop_back();
        }
        return sb;
    }

    void recursion(string & curr, int num) {
        if (num == 0) {
            return;
        } else if (num < 10) {
            curr = curr + singles[num] + " ";
        } else if (num < 20) {
            curr = curr + teens[num - 10] + " ";
        } else if (num < 100) {
            curr = curr + tens[num / 10] + " ";
            recursion(curr, num % 10);
        } else {
            curr = curr + singles[num / 100] + " Hundred ";
            recursion(curr, num % 100);
        }
    }
};