keyboard_row.txt

public class Solution {
    public String[] findWords(String[] words) {
        int topRow = 0;
        int middleRow = 0;
        int bottomRow = 0;
        Set<String> topLetters = new HashSet<String>(Arrays.asList("q", "w", "e", "r", "t", "y", "u", "i", "o", "p"));
        Set<String> middleLetters = new HashSet<String>(Arrays.asList("a", "s", "d", "f", "g", "h", "j", "k", "l"));
        Set<String> bottomLetters = new HashSet<String>(Arrays.asList("z", "x", "c", "v", "b", "n", "m"));
        Set<String> wordLetters = new HashSet<String>();
        List<String> oneLineableWords = new ArrayList<String>();
        for (String str : words) {
            for (char ch : str.toCharArray()) {
                wordLetters.add(Character.toString(ch).toLowerCase());
            }
            if (topLetters.containsAll(wordLetters) || middleLetters.containsAll(wordLetters) || bottomLetters.containsAll(wordLetters)) {
                oneLineableWords.add(str);
            }
            wordLetters.clear();
        }
        
        String[] stringArray = oneLineableWords.toArray(new String[0]);
        for (String str : oneLineableWords) {
            System.out.println(str);
        }
        return stringArray;
    }
}