Memory Game

import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

public class MemoryGame {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        List<String> sequenceOfElements = Arrays.stream(scanner.nextLine().split("\\s+")).collect(Collectors.toList());

        int twinElement = 0;
        String input = scanner.nextLine();
        while (!input.equals("end")) {
            twinElement++;
            String[] element = input.split("\\s+");
            int firstDigit = Integer.parseInt(element[0]);
            int secondDigit = Integer.parseInt(element[1]);
            boolean isValid = checkIsValid(sequenceOfElements, firstDigit, secondDigit, twinElement);
            if (isValid) {
                checkAndRemove(sequenceOfElements, firstDigit, secondDigit);
            }
            if (sequenceOfElements.isEmpty()) {
                System.out.printf("You have won in %d turns!%n", twinElement);
                return;
            }
            input = scanner.nextLine();
        }
        System.out.println("Sorry you lose :(");
        System.out.println(String.join(" ", sequenceOfElements));
    }

    private static void checkAndRemove(List<String> numberSequence, int numberOne, int numberTwo) {
        if (numberSequence.get(numberOne).equals(numberSequence.get(numberTwo))) {
            System.out.printf("Congrats! You have found matching elements - %s!%n", numberSequence.get(numberOne));
            String currentElement = numberSequence.get(numberOne);
            for (int i = 0; i < numberSequence.size(); i++) {
                if (numberSequence.get(i).equals(currentElement)) {
                    numberSequence.remove(i);
                    i = -1;
                }
            }
        } else {
            System.out.println("Try again!");
        }
    }

    private static boolean checkIsValid(List<String> numberSequence, int numberOne, int numberTwo, int moves) {
        if ((numberOne == numberTwo) ||
                (numberOne < 0) ||
                (numberTwo < 0) ||
                (numberOne >= numberSequence.size()) ||
                (numberTwo >= numberSequence.size())) {
            numberSequence.add(numberSequence.size() / 2, "-" + moves + "a");
            numberSequence.add(numberSequence.size() / 2 + 1, "-" + moves + "a");
            System.out.println("Invalid input! Adding additional elements to the board");
            return false;
        }
        return true;
    }
}