Write a function that takes a string as input and reverse only the vowels of a string.

Example 1: Given s = "hello", return "holle".

Example 2: Given s = "leetcode", return "leotcede".

思路: 用一个hash表存一下元音字符, 然后设置左右指针找到两个都是元音的位置交换一下就可以了. 注意字符是大小写都有的.

1 class Solution { 2 public: 3     string reverseVowels(string s) { 4         set
      
        hash{
    'a', 'e', 'o', 'i', 'u','A', 'E', 'I', 'O', 'U'}; 5         int len = s.length(); 6         int left = 0, right = len - 1; 7         while(left < right){ 8             if(hash.count(s[left]) == 0) 9                 left++;10             if(hash.count(s[right]) == 0)11                 right--;12             if(hash.count(s[left]) != 0 && hash.count(s[right]) != 0 ){13                 swap(s[left], s[right]);14                 left++;15                 right--;16             }17         }18         return s;19         20     }21 };