示例 1:
​
输入: "hello"
输出: "holle"
示例 2:
​
输入: "leetcode"
输出: "leotcede"
说明:
元音字母不包含字母"y"。

class Solution {
set<char> vowels={'a','e','i','o','u','A','E','I','O','U'};
public:
    string reverseVowels(string s) {
        string res;
        // cout<<s.length()<<endl;
         if(!s.length()) return res;
        vector<int>indexs;
        for(int i=0;i<s.length();i++)
        {
            if(vowels.count(s[i])) indexs.push_back(i);
        }
        if(indexs.empty()) return s;
        // for(auto c:indexs)
        //     cout<<c<<" ";
        int start=0;
        for(int i=0;i<s.length();i++)
        {
            if(start <indexs.size() &&i==indexs[start]   )
            {
                res+=s[indexs[indexs.size()-1-start]];
                ++start;
            //    cout<<res<<endl;
            }
            else 
            {
                res+=s[i];
        //        cout<<res<<" -  "<<endl;
            }
​
        }
        return res;
    }
};