[Swift] Ascii
\n\nclass Solution { // 65 97\n    func greatestLetter(_ s: String) -> String {\n        var dic = [String:Int]()\n        var greatest: String = ""\n\n        
\n```\nclass Solution { // 65 97\n    func greatestLetter(_ s: String) -> String {\n        var dic = [String:Int]()\n        var greatest: String = ""\n\n        for c in s { \n            let char = c.lowercased()\n            let asc = Int(c.asciiValue!)\n            if let prevAsc = dic[char] { \n                if abs(prevAsc - asc) == 32 {\n                    greatest = max(greatest, c.uppercased())\n                }\n            } else { \n                dic[char] = asc\n            }\n        }\n        return greatest\n    }\n}\n```
['Swift']