Beginner friendly [Java/JavaScript/Python] Solution
Time Complexity :  O(n)\nJava\n\nclass Solution {\n    public int countVowelStrings(int n) {\n        int a=1, e=1, i=1, o=1, u=1;\n        while(n-- > 1){\n   
**Time Complexity :  O(n)**\n**Java**\n```\nclass Solution {\n    public int countVowelStrings(int n) {\n        int a=1, e=1, i=1, o=1, u=1;\n        while(n-- > 1){\n            a = a + e + i + o + u;\n            e = e + i + o + u;\n            i = i + o + u;\n            o = o + u;\n            u = u;\n        }\n        return a + e + i + o + u;\n    }\n}\n```\n**JavaScript**\n```\nvar countVowelStrings = function(n) {\n    let a=1, e=1, i=1, o=1, u=1\n    while(n-- > 1){\n        a = a + e + i + o + u\n        e = e + i + o + u\n        i = i + o + u\n        o = o + u\n        u = u\n    }\n    return a + e + i + o + u\n};\n```\n**Python**\n```\nclass Solution(object):\n    def countVowelStrings(self, n):\n        a,e,i,o,u = 1,1,1,1,1\n        for x in range(n-1):\n            a = a + e + i + o + u\n            e = e + i + o + u\n            i = i + o + u\n            o = o + u\n            u = u\n        return a + e + i + o + u\n```
['Python', 'Java', 'JavaScript']