Mathematical Approach
hint draw venn diagram and try finding permutation\nwe will get answer by\nall permutations - (e0 + l0 + t0 + e1 - e0l0 - e0t0 - l0t0 -l0e1 - t0e1 + e1l0t0 + e0
hint draw venn diagram and try finding permutation\nwe will get answer by\nall permutations - (e0 + l0 + t0 + e1 - e0l0 - e0t0 - l0t0 -l0e1 - t0e1 + e1l0t0 + e0l0t0)\n\nwhere xi means x comes i number of times so e1l0t0 means 1 e 0 l 0 t\n# Code\n```\nclass Solution:\n    def stringCount(self, n: int) -> int:\n        if(n<4):\n            return 0\n        a=26**n\n        b=25**n\n        c=24**n\n        d=23**n\n        return ((a)-(3*b+(n*(b//25))-3*c-(2*n*(c//24))+d+(n*(d//23))))%1000000007\n
['Math', 'Python3']