2309. Greatest English Letter in Upper and Lower Case

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problem

solution

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class Solution {
public:
    string greatestLetter(string s) {
        vector<int> lower(26,0), upper(26,0);
        for(char c:s){
            if(c>=65 && c<=90) upper[c-'A']++;
            else lower[c-'a']++;
        }
        for(int i=25;i>-1;--i){
            if(lower[i]>0 && upper[i]>0){
                
                return string(1, 'A'+i);
            }
        }
        return "";
    }
};

analysis

  • time complexity O(n)
  • space complexity O(1)