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".

class Solution {
public:
    string reverseVowels(string s) {
        char arr[] = {'a', 'e','i','o','u','A','E','I','O','U'};
        vector<char> v = vector<char>();
        set<char> vowels = set<char>(arr, arr+10);
        for(int i=0;i<s.size();i++)
            if(vowels.count(s[i]) > 0)
                v.push_back(s[i]);
        for(int i=0,j=v.size()-1;i<s.size() && j>=0;i++)
            if(vowels.count(s[i]) > 0)
                s[i] = v[j--];
        return s;
    }
};