public class Solution {
    private List<String> keyboardRows;
    private StringBuilder wordsPossibleToBuildUsingKeyboardRows;

    public Solution() {
        this.keyboardRows = new ArrayList<>();
        keyboardRows.add("qwertyuiop");
        keyboardRows.add("asdfghjkl");
        keyboardRows.add("zxcvbnm");

        wordsPossibleToBuildUsingKeyboardRows = new StringBuilder();
    }

    public String[] findWords(String[] words) {


        for (String word:words) {

            for (String keyboardRow:keyboardRows) {

                if(checkIfCanBuildAWordInAGivenRow(word,keyboardRow)){
                   wordsPossibleToBuildUsingKeyboardRows.append(word+",");

                }
            }

        }





        if(wordsPossibleToBuildUsingKeyboardRows.toString().equals("")){

            return new String[]{};
        }
        else {
            return wordsPossibleToBuildUsingKeyboardRows.toString().split(",");
        }

    }

    private boolean checkIfCanBuildAWordInAGivenRow(String word, String keyboardRow) {
        word = word.toLowerCase();
        for(int i = 0 ; i<word.length();i++){
            char  currentLetter = word.charAt(i);
            if(!keyboardRow.contains(String.valueOf(currentLetter))){
                return false;
            }
        }

        return true;
    }
}