Easy Python Solution
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        s=set(s)\n        a=[]\n        for i in s:\n            if(i.isupper()):\n                if(i.lower() in s):\n                    a.append(i)\n        if(len(a)==0):\n            return ""\n        return sorted(a)[-1]\n```
['Python3']