Simple Python Solution
Since they asked the uppercase character that is appeared in the given array in both uppercase and lowercase, we can use array of uppercase alphabets to solve t
Since they asked the uppercase character that is appeared in the given array in both uppercase and lowercase, we can use array of uppercase alphabets to solve this.\nIt is faster than 93.57% of Python3 submissions.\n\n```\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        l=[\'A\',\'B\',\'C\',\'D\',\'E\',\'F\',\'G\',\'H\',\'I\',\'J\',\'K\',\'L\',\'M\',\'N\',\'O\',\'P\',\'Q\',\'R\',\'S\',\'T\',\'U\',\'V\',\'W\',\'X\',\'Y\',\'Z\']\n        for i in l[::-1]:\n            if i.lower() in s and i in s:\n                return i\n        return ""\n        \n```
['Python3']