Greatest English Letter in Upper and Lower Case
```class Solution {\npublic:\n    bool check_small(char c){\n        return c>=97 && c<=122;\n    }\n    string greatestLetter(string s) {\n        unordered_ma
```class Solution {\npublic:\n    bool check_small(char c){\n        return c>=97 && c<=122;\n    }\n    string greatestLetter(string s) {\n        unordered_map<char ,int> mp;\n        for(auto i:s){\n            mp[i]++;\n        }\n        int max_ans = INT_MIN;\n        string ans  ="";\n        for(auto i:s){\n            if(check_small(i)){\n                if(mp[toupper(i)]>0){\n                    if((int)(i-\'a\') > max_ans){\n                        max_ans =(int)(i-\'a\');\n                        ans = toupper(i);\n                    }\n                }\n            }\n        }\n        return ans;\n        \n        \n    }\n};
['C']