Python solution 100%
Intuition\n Describe your first thoughts on how to solve this problem. \n1. Use a set to eliminate duplicates\n2. Create an empty array \n3. Loop through the st
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n1. Use a set to eliminate duplicates\n2. Create an empty array \n3. Loop through the string checking whether the character is in lowercase or upper case\n4. Check whether the opposite of that letter in in the string (eg. if lowercase, check uppercase)\n5. Append the capital of that letter to the result array\n6. Find the greatest letter amongst the solutions\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(object):\n    def greatestLetter(self, s):\n        s = set(s)\n        result = []\n        for letter in s:\n            if letter == letter.lower():\n                if letter.upper() in s:\n                    result.append(letter.upper())\n            else:\n                if letter.lower() in s:\n                    result.append(letter)\n        if not result:\n            return ""\n            \n        return max(result)\n\n\n        \n```
['Python']