[Python] simple DP solution - O(N) / O(1)
Python\nclass Solution:\n    def countVowelStrings(self, n: int) -> int:\n        \n        a = e = i = o = u = 1\n        for _ in range(n - 1):\n            a
```Python\nclass Solution:\n    def countVowelStrings(self, n: int) -> int:\n        \n        a = e = i = o = u = 1\n        for _ in range(n - 1):\n            a, e, i, o, u = a+e+i+o+u, e+i+o+u, i+o+u, o+u, u\n        \n        return a+e+i+o+u\n```
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