Simple Solution || Easy Understanding
\n//Please do upvote, if you like my solution :)\nclass Solution {\npublic:\n    int ans = 0;\n    void solve(int n,vector<char> &v,int idx){\n        if(n == 0
```\n//Please do upvote, if you like my solution :)\nclass Solution {\npublic:\n    int ans = 0;\n    void solve(int n,vector<char> &v,int idx){\n        if(n == 0){\n            ans++;\n            return;\n        }\n        if(idx >= v.size()) return;\n        solve(n-1,v,idx);\n        solve(n,v,idx+1);\n    }\n    int countVowelStrings(int n) {\n        vector<char> v = {\'a\',\'e\',\'i\',\'o\',\'u\'};\n        solve(n,v,0);\n        return ans;\n    }\n};\n//Please do upvote, if you like my solution :)\n```
['Backtracking', 'Recursion', 'C', 'C++']