class Solution {
    public String[] findWords(String[] words) {
        ArrayList<String> res = new ArrayList<String>();
        HashSet<Character> top = new HashSet<Character>();
        String a = "qwertyuiopQWERTYUIOP";
        for (int i = 0; i < a.length(); i++){
            top.add(a.charAt(i));
        }
        HashSet<Character> mid = new HashSet<Character>();
        String b = "asdfghjklASDFGHJKL";
        for (int i = 0; i < b.length(); i++){
            mid.add(b.charAt(i));
        }
        HashSet<Character> bot = new HashSet<Character>();
        String c = "zxcvbnmZXCVBNM";
        for (int i = 0; i < c.length(); i++){
            bot.add(c.charAt(i));
        }

        for (int i = 0; i < words.length; i++){
            int wordLength = words[i].length();
            int checkTop = 0;
            int checkMid = 0;
            int checkBot = 0;
            for (int j = 0; j < words[i].length(); j++){
                if (top.contains(words[i].charAt(j))){
                    checkTop++;
                }
                else if (mid.contains(words[i].charAt(j))){
                    checkMid++;
                }
                else{
                    checkBot++;
                }
            }
            if (checkTop == wordLength || checkMid == wordLength || checkBot == wordLength){
                res.add(words[i]);
            }
            checkTop = 0;
            checkMid = 0;
            checkBot = 0;
        }
        String[] result = new String[res.size()];
        return res.toArray(result);
    }
}