[Javascript] SET
Create a set of unique letters in s, then check from Z to A.\n\n\nvar greatestLetter = function(s) {\n    let set=new Set(s.split(""));\n\t// ASCII(A-Z, a-z)=(6
Create a `set` of unique letters in `s`, then check from `Z` to `A`.\n\n```\nvar greatestLetter = function(s) {\n    let set=new Set(s.split(""));\n\t// ASCII(A-Z, a-z)=(65-90, 97-122).\n    for(let i=90; i>=65; i--){\n        if(set.has(String.fromCharCode(i)) && set.has(String.fromCharCode(i+32))){\n            return String.fromCharCode(i);\n        }\n    }\n    return "";\n};\n```\n\nThanks for your reading and **up-voting** :)\n\n**\u2B50 Check [HERE](https://github.com/Lynn19950915/LeetCode_King) for my full Leetcode Notes ~**
['Ordered Set', 'JavaScript']