/*
* The MIT License (MIT)
*
* FXGL - JavaFX Game Library
*
* Copyright (c) 2015-2017 AlmasB (almaslvl@gmail.com)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package com.almasb.fxglgames.tictactoe.control.enemy;
import com.almasb.fxgl.app.FXGL;
import com.almasb.fxglgames.tictactoe.TicTacToeApp;
import com.almasb.fxglgames.tictactoe.TileEntity;
import com.almasb.fxglgames.tictactoe.TileValue;
import java.util.ArrayList;
import java.util.List;
/**
* The minimax algorithm is adapted from
* https://www.ntu.edu.sg/home/ehchua/programming/java/JavaGame_TicTacToe_AI.html
*
* @author Almas Baimagambetov (almaslvl@gmail.com)
*/
public class MinimaxControl extends EnemyControl {
private TileValue mySeed = TileValue.O;
private TileValue oppSeed = TileValue.X;
private TileValue[][] cells = new TileValue[3][3];
@Override
public void makeMove() {
TileEntity[][] board = FXGL.<TicTacToeApp>getAppCast().getBoard();
// the algorithm uses [row][col]
for (int y = 0; y < 3; y++) {
for (int x = 0; x < 3; x++) {
cells[y][x] = board[x][y].getValue();
}
}
int[] result = minimax(2, mySeed); // depth, max turn
board[result[2]][result[1]].getControl().mark(mySeed);
}
/** Recursive minimax at level of depth for either maximizing or minimizing player.
Return int[3] of {score, row, col} */
private int[] minimax(int depth, TileValue player) {
// Generate possible next moves in a List of int[2] of {row, col}.
List<int[]> nextMoves = generateMoves();
// mySeed is maximizing; while oppSeed is minimizing
int bestScore = (player == mySeed) ? Integer.MIN_VALUE : Integer.MAX_VALUE;
int currentScore;
int bestRow = -1;
int bestCol = -1;
if (nextMoves.isEmpty() || depth == 0) {
// Gameover or depth reached, evaluate score
bestScore = evaluate();
} else {
for (int[] move : nextMoves) {
// Try this move for the current "player"
cells[move[0]][move[1]] = player;
if (player == mySeed) { // mySeed (computer) is maximizing player
currentScore = minimax(depth - 1, oppSeed)[0];
if (currentScore > bestScore) {
bestScore = currentScore;
bestRow = move[0];
bestCol = move[1];
}
} else { // oppSeed is minimizing player
currentScore = minimax(depth - 1, mySeed)[0];
if (currentScore < bestScore) {
bestScore = currentScore;
bestRow = move[0];
bestCol = move[1];
}
}
// Undo move
cells[move[0]][move[1]] = TileValue.NONE;
}
}
return new int[] {bestScore, bestRow, bestCol};
}
/** Find all valid next moves.
Return List of moves in int[2] of {row, col} or empty list if gameover */
private List<int[]> generateMoves() {
List<int[]> nextMoves = new ArrayList<int[]>(); // allocate List
// If gameover, i.e., no next move
if (hasWon(mySeed) || hasWon(oppSeed)) {
return nextMoves; // return empty list
}
// Search for empty cells and add to the List
for (int row = 0; row < 3; ++row) {
for (int col = 0; col < 3; ++col) {
if (cells[row][col] == TileValue.NONE) {
nextMoves.add(new int[] {row, col});
}
}
}
return nextMoves;
}
/** The heuristic evaluation function for the current board
@Return +100, +10, +1 for EACH 3-, 2-, 1-in-a-line for computer.
-100, -10, -1 for EACH 3-, 2-, 1-in-a-line for opponent.
0 otherwise */
private int evaluate() {
int score = 0;
// Evaluate score for each of the 8 lines (3 rows, 3 columns, 2 diagonals)
score += evaluateLine(0, 0, 0, 1, 0, 2); // row 0
score += evaluateLine(1, 0, 1, 1, 1, 2); // row 1
score += evaluateLine(2, 0, 2, 1, 2, 2); // row 2
score += evaluateLine(0, 0, 1, 0, 2, 0); // col 0
score += evaluateLine(0, 1, 1, 1, 2, 1); // col 1
score += evaluateLine(0, 2, 1, 2, 2, 2); // col 2
score += evaluateLine(0, 0, 1, 1, 2, 2); // diagonal
score += evaluateLine(0, 2, 1, 1, 2, 0); // alternate diagonal
return score;
}
/** The heuristic evaluation function for the given line of 3 cells
@Return +100, +10, +1 for 3-, 2-, 1-in-a-line for computer.
-100, -10, -1 for 3-, 2-, 1-in-a-line for opponent.
0 otherwise */
private int evaluateLine(int row1, int col1, int row2, int col2, int row3, int col3) {
int score = 0;
// First cell
if (cells[row1][col1] == mySeed) {
score = 1;
} else if (cells[row1][col1] == oppSeed) {
score = -1;
}
// Second cell
if (cells[row2][col2] == mySeed) {
if (score == 1) { // cell1 is mySeed
score = 10;
} else if (score == -1) { // cell1 is oppSeed
return 0;
} else { // cell1 is empty
score = 1;
}
} else if (cells[row2][col2] == oppSeed) {
if (score == -1) { // cell1 is oppSeed
score = -10;
} else if (score == 1) { // cell1 is mySeed
return 0;
} else { // cell1 is empty
score = -1;
}
}
// Third cell
if (cells[row3][col3] == mySeed) {
if (score > 0) { // cell1 and/or cell2 is mySeed
score *= 10;
} else if (score < 0) { // cell1 and/or cell2 is oppSeed
return 0;
} else { // cell1 and cell2 are empty
score = 1;
}
} else if (cells[row3][col3] == oppSeed) {
if (score < 0) { // cell1 and/or cell2 is oppSeed
score *= 10;
} else if (score > 1) { // cell1 and/or cell2 is mySeed
return 0;
} else { // cell1 and cell2 are empty
score = -1;
}
}
return score;
}
private int[] winningPatterns = {
0b111000000, 0b000111000, 0b000000111, // rows
0b100100100, 0b010010010, 0b001001001, // cols
0b100010001, 0b001010100 // diagonals
};
/** Returns true if thePlayer wins */
private boolean hasWon(TileValue thePlayer) {
int pattern = 0b000000000; // 9-bit pattern for the 9 cells
for (int row = 0; row < 3; ++row) {
for (int col = 0; col < 3; ++col) {
if (cells[row][col] == thePlayer) {
pattern |= (1 << (row * 3 + col));
}
}
}
for (int winningPattern : winningPatterns) {
if ((pattern & winningPattern) == winningPattern) return true;
}
return false;
}
}