Python Solution || Beats 86% || Easy to understand
\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        \n        new = ""\n        \n        for i in s:\n            if i.isupper() and i.low
```\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        \n        new = ""\n        \n        for i in s:\n            if i.isupper() and i.lower() in s:\n                if i>new:\n                    new = i.upper()\n                        \n        return new\n\t\t\n```\t\t
['Python']