import java.util.ArrayList;
import java.util.List;

public class KeyboardRow {

    public static boolean checkRow(String row, String input) {
        boolean result = false;
        // check for row
        for (int i = 0; i < input.length(); i++) {
            if ( (row.indexOf(input.charAt(i))) != -1 ){
                if (i == input.length()-1) {
                    return true;
                }
            } else if ( (row.indexOf(input.charAt(i))) == -1 ){
                return false;
            }
        }
        return result;
    }

    public static String[] findWords(String[] words) {
        List<String> result = new ArrayList<>();
        String row1 = "qwertyuiopQWERTYUIOP";
        String row2 = "asdfghjklASDFGHJKL";
        String row3 = "zxcvbnmZXCVBNM";

        for (int i = 0; i < words.length; i++) {
            String currentString = words[i];
            if (checkRow(row1,currentString) || checkRow(row2,currentString) || checkRow(row3,currentString)){
                result.add(words[i]);
            }
        }
        return result.toArray(new String[0]);
    }

    public static void main(String[] args) {
        String[] words = {"Hello", "Alaska", "Dad", "Peace"};
        String[] result = findWords(words);
        for (int i = 0; i < result.length; i++) {
            System.out.println(result[i]);
        }
    }
}