在上一部分中，我们为井字游戏棋盘创建了一个 JavaScript 类。让我们在这部分学习如何在 JavaScript 中实现极小极大算法，以便为计算机玩家获得最佳移动。给定一些假设和深度（要计算的转数），我们将计算每个可能的移动的启发式值。

import Board from "./board.js";export default class Player {constructor(maxDepth = -1) {this.maxDepth = maxDepth;this.nodesMap = new Map();}
}

getBestMove(board, maximizing = true, callback = () => {}, depth = 0) {//clear nodesMap if the function is called for a new moveif(depth == 0) this.nodesMap.clear();//If the board state is a terminal one, return the heuristic valueif(board.isTerminal() || depth === this.maxDepth ) {if(board.isTerminal().winner === 'x') {return 100 - depth;} else if (board.isTerminal().winner === 'o') {return -100 + depth;}return 0;}
}

if (maximizing) {//Initialize best to the lowest possible valuelet best = -100;//Loop through all empty cellsboard.getAvailableMoves().forEach(index => {//Initialize a new board with a copy of our current stateconst child = new Board([...board.state]);//Create a child node by inserting the maximizing symbol x into the current empty cellchild.insert("x", index);//Recursively calling getBestMove this time with the new board and minimizing turn and incrementing the depthconst nodeValue = this.getBestMove(child, false, callback, depth + 1);//Updating best valuebest = Math.max(best, nodeValue);//If it's the main function call, not a recursive one, map each heuristic value with it's moves indicesif (depth == 0) {//Comma separated indices if multiple moves have the same heuristic valueconst moves = this.nodesMap.has(nodeValue)? `${this.nodesMap.get(nodeValue)},${index}`: index;this.nodesMap.set(nodeValue, moves);}});//If it's the main call, return the index of the best move or a random index if multiple indices have the same valueif (depth == 0) {if (typeof this.nodesMap.get(best) == "string") {const arr = this.nodesMap.get(best).split(",");const rand = Math.floor(Math.random() * arr.length);const ret = arr[rand];} else {ret = this.nodesMap.get(best);}//run a callback after calculation and return the indexcallback(ret);return ret;}//If not main call (recursive) return the heuristic value for next calculationreturn best;
}

import Board from "./board.js";export default class Player {constructor(maxDepth = -1) {this.maxDepth = maxDepth;this.nodesMap = new Map();}getBestMove(board, maximizing = true, callback = () => {}, depth = 0) {//clear nodesMap if the function is called for a new moveif (depth == 0) this.nodesMap.clear();//If the board state is a terminal one, return the heuristic valueif (board.isTerminal() || depth === this.maxDepth) {if (board.isTerminal().winner === "x") {return 100 - depth;} else if (board.isTerminal().winner === "o") {return -100 + depth;}return 0;}if (maximizing) {//Initialize best to the lowest possible valuelet best = -100;//Loop through all empty cellsboard.getAvailableMoves().forEach(index => {//Initialize a new board with a copy of our current stateconst child = new Board([...board.state]);//Create a child node by inserting the maximizing symbol x into the current empty cellchild.insert("x", index);//Recursively calling getBestMove this time with the new board and minimizing turn and incrementing the depthconst nodeValue = this.getBestMove(child, false, callback, depth + 1);//Updating best valuebest = Math.max(best, nodeValue);//If it's the main function call, not a recursive one, map each heuristic value with it's moves indicesif (depth == 0) {//Comma separated indices if multiple moves have the same heuristic valueconst moves = this.nodesMap.has(nodeValue)? `${this.nodesMap.get(nodeValue)},${index}`: index;this.nodesMap.set(nodeValue, moves);}});//If it's the main call, return the index of the best move or a random index if multiple indices have the same valueif (depth == 0) {let returnValue;if (typeof this.nodesMap.get(best) == "string") {const arr = this.nodesMap.get(best).split(",");const rand = Math.floor(Math.random() * arr.length);returnValue = arr[rand];} else {returnValue = this.nodesMap.get(best);}//run a callback after calculation and return the indexcallback(returnValue);return returnValue;}//If not main call (recursive) return the heuristic value for next calculationreturn best;}if (!maximizing) {//Initialize best to the highest possible valuelet best = 100;//Loop through all empty cellsboard.getAvailableMoves().forEach(index => {//Initialize a new board with a copy of our current stateconst child = new Board([...board.state]);//Create a child node by inserting the minimizing symbol o into the current empty cellchild.insert("o", index);//Recursively calling getBestMove this time with the new board and maximizing turn and incrementing the depthlet nodeValue = this.getBestMove(child, true, callback, depth + 1);//Updating best valuebest = Math.min(best, nodeValue);//If it's the main function call, not a recursive one, map each heuristic value with it's moves indicesif (depth == 0) {//Comma separated indices if multiple moves have the same heuristic valueconst moves = this.nodesMap.has(nodeValue)? this.nodesMap.get(nodeValue) + "," + index: index;this.nodesMap.set(nodeValue, moves);}});//If it's the main call, return the index of the best move or a random index if multiple indices have the same valueif (depth == 0) {let returnValue;if (typeof this.nodesMap.get(best) == "string") {const arr = this.nodesMap.get(best).split(",");const rand = Math.floor(Math.random() * arr.length);returnValue = arr[rand];} else {returnValue = this.nodesMap.get(best);}//run a callback after calculation and return the indexcallback(returnValue);return returnValue;}//If not main call (recursive) return the heuristic value for next calculationreturn best;}}
}

import Board from "./classes/board.js";
import Player from "./classes/player.js";const board = new Board(["x", "o", "", "", "", "", "o", "", "x"]);
board.printFormattedBoard();
const p = new Player();
console.log(p.getBestMove(board));
console.log(p.nodesMap);

import Board from "./classes/board.js";
import Player from "./classes/player.js";const board = new Board(["x", "o", "", "", "", "", "o", "", "x"]);
board.printFormattedBoard();
const p = new Player();
console.log(p.getBestMove(board, false)); //false for minimizing turn
console.log(p.nodesMap);