TicTacToe.java

import java.util.*;
import java.util.Scanner;

class Logic {
    static class Move {
        final int position;
        final int score;

        Move(int position, int score) {
            this.position = position;
            this.score = score;
        }
    }


    public static class TicTacToe {
        private final int[] board = new int[9];

        private final int emptySpace = 0;
        private final int playerAI = 1;
        private final int playerHuman = 2;

        private List<Integer> possibleMoves() {
            ArrayList<Integer> res = new ArrayList<>();
            for (int i = 0; i < 9; i++) {
                if (board[i] == emptySpace)
                    res.add(i);
            }
            return res;
        }

        private boolean win(int player) {
            return (board[0] == player && board[1] == player && board[2] == player) ||
                   (board[3] == player && board[4] == player && board[5] == player) ||
                   (board[6] == player && board[7] == player && board[8] == player) ||
                   (board[0] == player && board[3] == player && board[6] == player) ||
                   (board[1] == player && board[4] == player && board[7] == player) ||
                   (board[2] == player && board[5] == player && board[8] == player) ||
                   (board[0] == player && board[4] == player && board[8] == player) ||
                   (board[2] == player && board[4] == player && board[6] == player);
        }

        private Move mechanics(int player) {
            int otherPlayer = 3 - player;

            if (win(player))
                return new Move(-1, 10);
            if (win(otherPlayer))
                return new Move(-1, -10);

            List<Integer> possibleMoves = possibleMoves();
            if (possibleMoves.isEmpty())
                return new Move(-1, 0);

            Move bestMove = null;
            for (int move : possibleMoves) {
                board[move] = player;
                Move result = mechanics(otherPlayer);
                board[move] = emptySpace;

                if (bestMove == null || bestMove.score < -result.score) {
                    bestMove = new Move(move, -result.score);
                }
            }

            return bestMove;
        }

        public void printTable() {
            System.out.println(board[0] + " | " + board[1] + " | " + board[2]);
            System.out.println("-   -   -");
            System.out.println(board[3] + " | " + board[4] + " | " + board[5]);
            System.out.println("-   -   -");
            System.out.println(board[6] + " | " + board[7] + " | " + board[8]);
            System.out.println();
        }


        public void startGame() {
            int currentPlayer = playerHuman;

            Scanner ulaz = new Scanner(System.in);
            while (true) {
                printTable();
                if (win(playerHuman)) {
                    System.out.println("YOU WIN!");
                    break;
                }
                if (win(playerAI)) {
                    System.out.println("YOU LOSE!");
                    break;
                }
                if (possibleMoves().isEmpty()) {
                    System.out.println("DRAW");
                    break;
                }

                if (currentPlayer == playerHuman) {
                    board[ulaz.nextInt()] = playerHuman;
                } else {
                    Move move = mechanics(playerAI);
                    if (move.position >= 0) {
                        board[move.position] = playerAI;
                    } else {
                        break;
                    }
                }
                currentPlayer = 3 - currentPlayer;
            }
        }
    }

    public static void main(String[] args) {
        TicTacToe game = new TicTacToe();
        game.startGame();
    }
}