📌Fastest Java☕ Solution using HashSet💯
```\nclass Solution {\n    public String greatestLetter(String s) {\n        HashSet hset = new HashSet<>();\n        for(char ch : s.toCharArray())\n          
```\nclass Solution {\n    public String greatestLetter(String s) {\n        HashSet<Character> hset = new HashSet<>();\n        for(char ch : s.toCharArray())\n            hset.add(ch);\n        \n        for(char ch = \'Z\'; ch >= \'A\'; ch--)\n            if(hset.contains(ch) && hset.contains(Character.toLowerCase(ch)))\n               return ch+"";\n        return "";\n    }\n}
['Java']