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