Java minmax算法返回空移动，并且无法正确地撤消移动
这里是我的minmax算法的代码：
private static void minmax(){
Move move = max(4, true, null);
//System.out.println(move);
board.makeMove(move.getFromPoint(), move.getToPoint());
}
private static Move max(int depth, boolean player, Move passedMove){
if(depth == 0) return passedMove.setScore(board.boardVal());
Move max = new Move(Integer.MIN_VALUE);
for(int i = 0; i < board.getMoves(player).size(); i++){
Move move = board.getMoves(player).get(i);
board.makeMove(move.getFromPoint(), move.getToPoint());
//System.out.println(board);
Move scoreMove = min(depth - 1, !player, move);
board.undo();
if(scoreMove.getScore() > max.getScore()) max = new Move(move.getFromPoint(), move.getToPoint(), scoreMove.getScore());
}
return max;
}
private static Move min(int depth, boolean player, Move passedMove){
if(depth == 0) return passedMove.setScore(-board.boardVal());
Move min = new Move(Integer.MAX_VALUE);
for(int i = 0; i < board.getMoves(player).size(); i++){
Move move = board.getMoves(player).get(i);
board.makeMove(move.getFromPoint(), move.getToPoint());
//System.out.println(board);
Move scoreMove = max(depth - 1, !player, move);
board.undo();
if(scoreMove.getScore() < min.getScore()) min = new Move(move.getFromPoint(), move.getToPoint(), scoreMove.getScore());
}
return min;
}
移动是一个对象，用于存储从位置，到位置和与移动后的棋盘值相关的分数。 Move move = max(4, true, null); 将一个空值赋给“移动”（我不明白为什么），并且在这些方法运行后，它使板子处于一种奇怪的状态，似乎这些移动没有正确地被撤消，但我已经反复检查过这个功能。
这是一个运行代码的例子（在注释掉board.makeMove(move.getFromPoint(), move.getToPoint());行以防止空指针异常之后）：
8 [R] [N] [B] [Q] [K] [B] [N] [R]
7 [P] [P] [P] [P] [P] [P] [P] [P]
6 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
5 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
4 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
3 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
2 [P] [P] [P] [P] [P] [P] [P] [P]
1 [R] [N] [B] [Q] [K] [B] [N] [R]
a b c d e f g h
a2,a4
8 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
7 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
6 [ ] [ ] [ ] [ ] [ ] [ ] [N] [ ]
5 [ ] [ ] [N] [ ] [ ] [ ] [R] [K]
4 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
3 [ ] [ ] [ ] [ ] [ ] [ ] [B] [B]
2 [ ] [P] [ ] [ ] [ ] [ ] [ ] [ ]
1 [P] [ ] [R] [P] [P] [P] [P] [P]
a b c d e f g h
它只留下计算机的棋子，移除所有玩家的棋子。
移动类：
public class Move {
private Point fromPoint;
private Point toPoint;
private int score;
public Move(Point fromPoint, Point toPoint, int score){
this.fromPoint = fromPoint;
this.toPoint = toPoint;
this.score = score;
}
public Move(Point fromPoint, Point toPoint){
this(fromPoint, toPoint, 0);
}
public Move(int score){
this(null, null, score);
}
public Point getFromPoint() {
return fromPoint;
}
public Point getToPoint() {
return toPoint;
}
public int getScore() {
return score;
}
public Move setScore(int score){
this.score = score;
return this;
}
@Override
public String toString(){
return "(" + fromPoint.y + ", " + fromPoint.x + ")" + " (" + toPoint.y + ", " + toPoint.x + ") " + score;
}
}
Board类建立在二维数组的堆栈上，这里是移动和撤消方法：
public void makeMove(Point fromPoint, Point toPoint){
Piece[][] boardNode = new Piece[board.peek().length][];
for(int i = 0; i < boardNode.length; i++){ //this was changed
boardNode[i] = board.peek()[i].clone();
}
boardNode[fromPoint.y][fromPoint.x].setPoint(toPoint);
boardNode[toPoint.y][toPoint.x] = boardNode[fromPoint.y][fromPoint.x];
boardNode[fromPoint.y][fromPoint.x] = null;
board.push(boardNode);
}
public void undo(){
board.pop();
}
public ArrayList<Move> getMoves(boolean color){
ArrayList<Move> moves = new ArrayList<>();
for(Piece[] row : board.peek()){
for(Piece piece : row){
if(piece != null) {
for (Point point : piece.moves()) {
if (piece.getColor() == color && straightLine(piece.getPoint(), point) && (board.peek()[point.y][point.x] == null || board.peek()[point.y][point.x].getColor() != color)) moves.add(new Move(piece.getPoint(), point));
}
}
}
}
return moves;
}
我希望程序能够返回一个最佳移动（导致棋盘状态得分最高的移动）并离开棋盘，就像在minmax方法执行之前一样。 这两种情况都没有发生，该方法返回null，并且板完全更改。
在Board类中更改makeMove（）方法以正确复制板后，我现在正在使用该方法中的NullPointerExceptions：
8 [R] [N] [B] [Q] [K] [B] [N] [R]
7 [P] [P] [P] [P] [P] [P] [P] [P]
6 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
5 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
4 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
3 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
2 [P] [P] [P] [P] [P] [P] [P] [P]
1 [R] [N] [B] [Q] [K] [B] [N] [R]
a b c d e f g h
a2,a4
Exception in thread "main" java.lang.NullPointerException
at Board.makeMove(Board.java:45)
at ChessMain.min(ChessMain.java:87)
at ChessMain.max(ChessMain.java:75)
at ChessMain.min(ChessMain.java:89)
at ChessMain.max(ChessMain.java:75)
at ChessMain.minmax(ChessMain.java:63)
at ChessMain.play(ChessMain.java:58)
at ChessMain.main(ChessMain.java:15)
...
public abstract class Piece {
private boolean color;
private Point getPoint;
public Piece(int x, int y, boolean color){
this.color = color;
getPoint = new Point(x, y);
}
abstract int getValue();
public String toString(){
return "";
}
public void setPoint(Point point){
this.getPoint = point;
}
public Point getPoint(){ return getPoint; }
public boolean takable(Point point){ return containsPoint(moves(), point); }
private static boolean containsPoint(ArrayList<Point> list, Point point){
for(Point listPoint: list){
if(listPoint.x == point.x && listPoint.y == point.y) return true;
}
return false;
}
abstract ArrayList<Point> moves();
public boolean getColor(){ return color; }
}
下面是一个扩展Piece的对象的例子：
import java.util.ArrayList;
public class Bishop extends Piece{
public Bishop(int x, int y, boolean color) {
super(x, y, color);
}
public ArrayList<Point> moves(){
ArrayList<Point> possibleMoves = new ArrayList<>();
int x = 1;
while(getPoint().x + x <= 7 && getPoint().y + x <= 7){
possibleMoves.add(new Point(getPoint().x + x, getPoint().y + x));
x++;
}
x = 1;
while(getPoint().x - x >= 0 && getPoint().y + x <= 7){
possibleMoves.add(new Point(getPoint().x - x, getPoint().y + x));
x++;
}
x = 1;
while(getPoint().x - x >= 0 && getPoint().y - x >= 0){
possibleMoves.add(new Point(getPoint().x - x, getPoint().y - x));
x++;
}
x = 1;
while(getPoint().x + x <= 7 && getPoint().y - x >= 0){
possibleMoves.add(new Point(getPoint().x + x, getPoint().y - x));
x++;
}
return possibleMoves;
}
@Override
public String toString(){ return "B"; }
public int getValue(){ return 3;}
}
让我知道更多的信息会有所帮助。
任何帮助表示赞赏。
我可以看到一个问题：
public void makeMove(Point fromPoint, Point toPoint){
Piece[][] boardNode = board.peek(); // WARNING!!!
// Instead, make a copy of the previous board state
// so you don't change all board states when you want to change one.
boardNode[fromPoint.y][fromPoint.x].setPoint(toPoint);
boardNode[toPoint.y][toPoint.x] = boardNode[fromPoint.y][fromPoint.x];
boardNode[fromPoint.y][fromPoint.x] = null;
board.push(boardNode); // WARNING!!!
}
您的board在堆栈的每个级别使用相同的参考。
当你调用Piece[][] boardNode = board.peek(); ... board.push(boardNode); Piece[][] boardNode = board.peek(); ... board.push(boardNode); 你真的只是对所有的棋盘状态使用相同的参考，并修改其中的一个将修改所有这些参考的对象..我认为这不是你想要的。
这可能是您问题的根源，如果除此之外还有更多问题，请更新您的问题。
更新：
克隆棋盘状态的二维阵列仍然是个问题。 您克隆了数组，但不包括其中的Piece ，因此，当您更新该块的位置时，它会更新该板的所有状态所引用的对象。
首先，让Piece实现Cloneable
public abstract class Piece implements Cloneable {
// ...
@Override
public abstract Piece clone();
然后让所有的小孩Pieces实际克隆自己，例如Pawn做到这一点：
@Override
public Pawn clone() {
return new Pawn(getPoint.x, getPoint.y, color);
}
然后这个来克隆你的二维数组：
public void makeMove(Point fromPoint, Point toPoint) {
final Piece[][] prevBoard = board.peek();
final int width = prevBoard.length;
Piece[][] boardNode = new Piece[width][];
for (int i = 0; i < width; i++) {
final int height = prevBoard[i].length;
boardNode[i] = new Piece[height];
for (int j = 0; j < height; j++) {
Piece p = prevBoard[i][j];
if (p == null) {
boardNode[i][j] = null;
} else {
boardNode[i][j] = p.clone();
}
}
}
这似乎让你在正确的轨道上，但现在似乎对手正在移动球员片断，或类似的东西。
其余的祝你好运！
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