tic-tac-toe

Unbeatable Tic Tac Toe. Single-page HTML, CSS & JavaScript.

Implementation of Minimax algorithm wrapped up in a neat chalkboard UI. The chalk effect is achieved using SVG turbulence filters.

Minimax algorithm:

tic-tac-toe/index.html

Lines 438 to 482 in 3e10e64

	function getComputerMoveData(tempPlaygroundState, depth) {
	const winCombinationIndex = getWinCombinationIndex(tempPlaygroundState);
	if (winCombinationIndex !== -1) {
	// we've got a winner in this hypothetical game!
	const wonMover = tempPlaygroundState[winCombinations[winCombinationIndex][0]];
	return {
	index: -1,
	score: wonMover === 1
	? -1 // user hypothetically won (bad)
	: 1 // computer hypothetically won (good)
	};
	} else if (!tempPlaygroundState.some((mover) => mover === -1)) {
	// a tie
	return { index: -1, score: 0 };
	}
	depth = (depth || 0) + 1;
	// 1 - user's hypothetical turn; 0 - computer's hypothetical turn.
	const mover = +!(depth % 2);
	const availableMoves = tempPlaygroundState
	.map((_, i) => i)
	.filter((boardIndex) => tempPlaygroundState[boardIndex] === -1);
	const scores = [];
	const moves = [];
	for (let i = 0; i < availableMoves.length; i++) {
	const move = availableMoves[i];
	const iterationPlayground = [ ...tempPlaygroundState ];
	iterationPlayground[move] = mover;
	const hypotheticalMoveData = getComputerMoveData(iterationPlayground, depth);
	scores.push(hypotheticalMoveData.score);
	moves.push(move);
	// rollback the hypothetical move
	tempPlaygroundState[move] = -1;
	}
	const func = mover === 1
	? Math.min // we're looking for the min score if it's user's turn
	: Math.max; // and for the max score if it's computer's score
	const moveScore = func.apply(null, scores);
	const moveScoreIndex = scores.indexOf(moveScore);
	return { index: moves[moveScoreIndex], score: moveScore };
	}

DEMO