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

题目链接：https://leetcode.com/problems/integer-to-english-words/

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"

Hint:

Did you see a pattern in dividing the number into chunk of words? For example, 123 and 123000.
Group the number by thousands (3 digits). You can write a helper function that takes a number less than 1000 and convert just that chunk to words.
There are many edge cases. What are some good test cases? Does your code work with input such as 0? Or 1000010? (middle chunk is zero and should not be printed out)

思路：将其划分为几种情况递归处理，billion, million, thousand, hundred, ten, or others，并预先将数字对于的英文存储起来．

代码如下：

class Solution {
public:
string numberToWords(int num) {
if(num == 0) return "Zero";
return convert(num).substr(1);
}
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 "";
}
private:
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"};
};

参考：https://leetcode.com/discuss/57747/fairly-clear-4ms-c-solution