brute force || must see || easy to understand
Code\n\n#pragma GCC optimize("Ofast","inline","fast-math","unroll-loops","no-stack-protector")\n#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,
# Code\n```\n#pragma GCC optimize("Ofast","inline","fast-math","unroll-loops","no-stack-protector")\n#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native","f16c")\n\nstatic int fast_io = []() \n{ \n    std::ios::sync_with_stdio(false); \n    cin.tie(nullptr); \n    cout.tie(nullptr); \n    return 0; \n}();\n\n#ifdef LOCAL\n    freopen("input.txt", "r" , stdin);\n    freopen("output.txt", "w", stdout);\n#endif\n\nclass Solution {\npublic:\n    unordered_map<string,int>mp;\n    int maxFreq(string s, int maxLetters, int minSize, int maxSize) \n    {\n        //we have the string of the characters of lower case english letters\n\n        //we need to return the count of the substring\n        //the substring must have size at leat 1 and atmost 26\n\n        //it is possible to get the the substring of size 26 from every index i\n\n        for(int i=0;i<s.length();i++)\n        {\n            unordered_map<char,int>mp_size;\n            string temp="";\n\n            for(int j=i;j<(s.length());j++)\n            {\n                 mp_size[s[j]]++;\n                 temp.push_back(s[j]);\n                 \n                 if((mp_size.size() > maxLetters)  or (temp.length() > maxSize))\n                 {\n                     break;\n                 }\n\n                \n                 if((temp.length() >= minSize) and (temp.length() <= maxSize))\n                 {\n                      mp[temp]++;\n                 }\n            }\n        }\n        string ans_str ="";   \n        int ans_freq = 0;   \n        for(auto it = mp.begin() ; it!=mp.end() ; it++)\n        {\n            if(it->second > ans_freq)\n            {\n                ans_freq = it->second;\n                ans_str = it->first;\n            }\n        }\n        return ans_freq;\n    }\n};\n```
['Hash Table', 'String', 'Sliding Window', 'C++']