Video Explanation (Simple set theory)
Explanation\n\nClick here for the video\n\n# Code\n\ntypedef long long int ll;\n\nconst int MOD = 1e9+7;\n\nclass Solution {\n    \n    ll FastPower (ll a, ll b
# Explanation\n\n[Click here for the video](https://youtu.be/BR94gLASOOQ)\n\n# Code\n```\ntypedef long long int ll;\n\nconst int MOD = 1e9+7;\n\nclass Solution {\n    \n    ll FastPower (ll a, ll b) {\n        ll ans = 1;\n        while (b) {\n            if (b&1) ans = (ans * a) % MOD;\n            a = (a * a) % MOD;\n            b /= 2;\n        }\n        return ans;\n    }\n    \npublic:\n    int stringCount(int n) {\n        return (\n            FastPower(26, n)\n            -\n            (\n                (FastPower(25, n-1) * (n + 75)) % MOD \n                -\n                (FastPower(24, n-1) * (n*2 + 72)) % MOD\n                + \n                (FastPower(23, n-1) * (n + 23)) % MOD\n                + MOD\n            ) % MOD\n            + \n            MOD\n        ) % MOD;\n    }\n};\n```
['C++']