Python (Simple Maths)
\n    def greatestLetter(self, s):\n        res = ""\n        \n        for i in s:\n            if (i.islower() and i.upper() in s) or (i.isupper() and i.lower
\n    def greatestLetter(self, s):\n        res = ""\n        \n        for i in s:\n            if (i.islower() and i.upper() in s) or (i.isupper() and i.lower() in s):\n                res = max(res, i.upper())\n                \n        return res
[]