I’m currently trying to make a tic-tac-toe game using minimax algorithm. I’m using JavaScript with p5js framework for this project.
Here is the sketch.js code:
var rows = 3;
var cols = 3;
var scl = 1;
var board_width = cols * 100 * scl;
var board_height = rows * 100 * scl;
var board;
let player = 'x';
let ai = 'o';
let playerTurn;
let winner;
var resetBtn;
function setup() {
createCanvas(400, 300);
resetGame();
resetBtn = createButton("Reset");
resetBtn.position(320, 50);
resetBtn.size(60, 20);
}
function draw() {
resetBtn.mouseClicked(resetGame);
winner = checkWinner();
if (winner == 'x' || winner == 'o') {
console.log(winner);
}
else if (winner == 't') {
console.log("Tie");
}
else {
if (playerTurn == false) {
aiMove();
playerTurn = true;
}
}
drawBoard();
}
function mousePressed() {
if (playerTurn == true) {
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (mouseX > j * 100 && mouseX < (j * 100 + 100) && mouseY > i * 100 && mouseY < (i * 100 + 100)) {
board[i][j] = player;
playerTurn = false;
}
}
}
}
}
function aiMove() {
let bestScore = -2;
let score;
let moveSpot = [];
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (board[i][j] == ' ') {
board[i][j] = ai;
score = miniMax(board, false);
board[i][j] = ' ';
if (score > bestScore) {
bestScore = score;
moveSpot = {i, j};
}
}
}
}
board[moveSpot.i][moveSpot.j] = ai;
}
function miniMax(board, isMaximizing) {
let result = checkWinner();
if (result == 'x') {
return -1;
}
else if (result == 'o') {
return 1;
}
else if (result == 't') {
return 0;
}
else if (isMaximizing) {
let bestScore = -2;
let score;
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (board[i][j] == ' ') {
board[i][j] = ai;
score = miniMax(board, false);
board[i][j] = ' ';
bestScore = max(score, bestScore);
}
}
}
return bestScore;
}
else {
let bestScore = 2;
let score;
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (board[i][j] == ' ') {
board[i][j] = player;
score = miniMax(board, true);
board[i][j] = ' ';
bestScore = min(score, bestScore);
}
}
}
return bestScore;
}
}
function checkWinner() {
let w = null;
if (board[0][0] == 'x' && board[0][1] == 'x' && board[0][2] == 'x' ||
board[1][0] == 'x' && board[1][1] == 'x' && board[1][2] == 'x' ||
board[2][0] == 'x' && board[2][1] == 'x' && board[2][2] == 'x' ||
board[0][0] == 'x' && board[1][0] == 'x' && board[2][0] == 'x' ||
board[0][1] == 'x' && board[1][1] == 'x' && board[2][1] == 'x' ||
board[0][2] == 'x' && board[1][2] == 'x' && board[2][2] == 'x' ||
board[0][0] == 'x' && board[1][1] == 'x' && board[2][2] == 'x' ||
board[2][0] == 'x' && board[1][1] == 'x' && board[0][2] == 'x') {
return 'x';
}
else if (board[0][0] == 'o' && board[0][1] == 'o' && board[0][2] == 'o' ||
board[1][0] == 'o' && board[1][1] == 'o' && board[1][2] == 'o' ||
board[2][0] == 'o' && board[2][1] == 'o' && board[2][2] == 'o' ||
board[0][0] == 'o' && board[1][0] == 'o' && board[2][0] == 'o' ||
board[0][1] == 'o' && board[1][1] == 'o' && board[2][1] == 'o' ||
board[0][2] == 'o' && board[1][2] == 'o' && board[2][2] == 'o' ||
board[0][0] == 'o' && board[1][1] == 'o' && board[2][2] == 'o' ||
board[2][0] == 'o' && board[1][1] == 'o' && board[0][2] == 'o') {
return 'o';
}
let full = 0;
for (let i = 0; i < 3; i++) {
for (let j = 0; j < 3; j++) {
if (board[i][j] == 'x' || board[i][j] == 'o') {
full ++;
}
}
}
if (full == 9) {
return 't';
}
return winner;
return w;
}
function drawBoard() {
// draw board
stroke(0);
strokeWeight(7);
line(board_width / 3, 0, board_width / 3, board_height);
line(board_width / 3 * 2, 0, board_width / 3 * 2, board_height);
line(0, board_height / 3, board_width, board_height / 3);
line(0, board_height / 3 * 2, board_width, board_height / 3 * 2);
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (board[i][j] == 'o') {
circle(j * 100 + 50, i * 100 + 50, 80);
}
else if (board[i][j] == 'x') {
line(j * 100 + 10, i * 100 + 10, j * 100 + 80, i * 100 + 80);
line(j * 100 + 80, i * 100 + 10, j * 100 + 10, i * 100 + 80);
}
}
}
}
function resetGame() {
clear();
winner = null;
board = [];
playerTurn = true;
background(255);
for (let i = 0; i < rows; i++) {
let row = [];
for (let j = 0; j < cols; j++) {
row[j] = ' ';
}
board.push(row);
}
}
The problem is shown in the picture. As you, the player make first move, if you choose spot 2 then 4 then 6, the ai doesn’t go to spot 9 to win but go to spot 3 instead.
screenshot
I tried this tactic in an example on this website:
https://www.freecodecamp.org/news/how-to-make-your-tic-tac-toe-game-unbeatable-by-using-the-minimax-algorithm-9d690bad4b37/
and got similar result.
Is this a problem with the algorithm implementation or something else?
Thanks,
