[C++} Easy to understand Time : O(N) & Space : O(1)
\nclass Solution\n{\npublic:\n    int countVowelStrings(int n)\n    {\n        int a = 1, e = 1, i = 1, o = 1, u = 1;\n        for (int N = 2; N <= n; N++)\n   
```\nclass Solution\n{\npublic:\n    int countVowelStrings(int n)\n    {\n        int a = 1, e = 1, i = 1, o = 1, u = 1;\n        for (int N = 2; N <= n; N++)\n        {\n            u = a + e + i + o + u;\n            o = a + e + i + o;\n            i = a + e + i;\n            e = a + e;\n            a = a;\n        }\n        return a + e + i + o + u;\n    }\n};`\n```
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