ab.ts

/**
 * αβ法での探索
 */
const dive = (o: Othello, pos: number, alpha = -Infinity, beta = Infinity, depth = 0): number => {
	depth++;

	const undo = o.put(o.turn, pos, true);

	// 勝った
	if (o.turn === null) {
		const winner = o.winner;

		// 勝ちは勝ちでも、より相手の石を少なくした方が美しい勝ちだと判定する
		const score = botColor ? 10000 + (o.blackCount * 100) : 10000 + (o.whiteCount * 100);

		// 巻き戻し
		o.undo(undo);

		return winner === botColor ? score : -score;
	}

	if (depth === maxDepth) {
		let score = o.canPutSomewhere(botColor).length;

		mathsStrongs.forEach((s, i) => {
			s = s * 30;
			const stone = o.board[i];
			if (stone === botColor) {
				score += s;
			} else if (stone != null) {
				score -= s;
			}
		});

		// 巻き戻し
		o.undo(undo);

		return score;
	} else {
		const isNextBotTurn = o.turn === botColor;

		const cans = o.canPutSomewhere(o.turn);

		// 次のターンのプレイヤーにとって最も良い手を取得
		for (const p of cans) {
			const score = dive(o, p, alpha, beta, depth);

			if (isNextBotTurn) {
				alpha = Math.max(alpha, score);
				if (alpha >= beta) break;
			} else {
				beta = Math.min(beta, score);
				if (alpha >= beta) break;
			}
		}

		// 巻き戻し
		o.undo(undo);

		return isNextBotTurn ? alpha : beta;
	}
};