[Leetcode] 273. Integer to English Words 解题报告

题目：

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

For example,

123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

思路：

我原来用迭代实现的版本真的太长了。下面这个版本是递归的，非常简洁和好理解。

代码：

class Solution {
public:
string numberToWords(int num) {
if(num == 0) {
return "Zero";
}
return convert(num).substr(1);
}
private:
string convert(int num) {
if(num >= 1000000000) {
return convert(num / 1000000000) + " Billion" + convert(num - 1000000000 * (num / 1000000000));
}
if(num >= 1000000) {
return convert(num / 1000000) + " Million" + convert(num - 1000000 * (num / 1000000));
}
if(num >= 1000) {
return convert(num / 1000) + " Thousand" + convert(num - 1000 * (num / 1000));
}
if(num >= 100) {
return convert(num / 100) + " Hundred" + convert(num - 100 * (num / 100));
}
if(num >= 20) {
return " " + above20[num / 10 - 2] + convert(num - 10 * (num / 10));
}
if(num >= 1) {
return " " + below20[num - 1];
}
return "";
}
string above20[8] = {"Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
string below20[19] = {"One", "Two", "Three", "Four", "Five", "Six", "Seven",
"Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen",
"Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
};