LeetCode273. Integer to English Words

题目链接：

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

题目描述：

将整数转化成英语单词字符串

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”

题目分析：

好麻烦啊感觉，自己写的太挫，逻辑之混乱……真的就不贴出来了。

谢谢这位大神的，代码还是很简洁哒

http://www.cnblogs.com/grandyang/p/4772780.html

整数有范围限制，按英语的规则来，都是3个一组的读，所以我们也按3个一组分，最多可以分为4组。每次处理一个3位数，根据执行了多少次，后面判断是带“Thousand”还是”Million”还是”Billion”。

主要就是空格的处理，还有就是三位数中有0的时候的处理。当b<20时，可以直接从对应数组取。

代码：

class Solution {
public:
     vector<string> v1={"","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
     vector<string> v2={"","","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};
     vector<string> v3={"Hundred","Thousand", "Million", "Billion"};
    string numberToWords(int num) {
      if(num==0){
          return "Zero";
      }
      string result=numberToWordsHelper(num%1000);
      num/=1000;
      for(int i=1;i<=3;i++){
          result=num%1000? numberToWordsHelper(num%1000)+" "+v3[i]+" "+result:result;
          num/=1000;
      }
      while(result.back()==' '){
          result.pop_back();
      }
      return result;
    }
    string numberToWordsHelper(int num){
        string result="";
        int a=num/100;
        int b=num%100;
        int c=num%10;
        result= b<20 ? v1[b]:v2[b/10]+(c? " "+v1[c]:"");
        if(a>0){
            result=v1[a]+" "+v3[0]+(b?" "+result:"");
        }
        return result;
    }
};