我的 MCTS Gomoku 播放器的 Java 堆空间问题

问：

当我运行我的程序时，我收到以下错误：

Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: Java heap space
        at MCTSNode.setPossibleMoves(MCTSNode.java:66)
        at MCTSNode.Expand(MCTSNode.java:167)
        at MctsPlayer.getBestMove(MctsPlayer.java:39)
        at NewBoardGUI.btnClick(NewBoardGUI.java:617)
        at NewBoardGUI.lambda$createButton$0(NewBoardGUI.java:584)
        at NewBoardGUI$$Lambda$115/558922244.actionPerformed(Unknown Source)
        at java.desktop/javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at java.desktop/javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
        at java.desktop/java.awt.Component.processMouseEvent(Unknown Source)
        at java.desktop/javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.desktop/java.awt.Component.processEvent(Unknown Source)
        at java.desktop/java.awt.Container.processEvent(Unknown Source)
        at java.desktop/java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.desktop/java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.desktop/java.awt.Component.dispatchEvent(Unknown Source)
        at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.desktop/java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.desktop/java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.desktop/java.awt.Component.dispatchEvent(Unknown Source)
        at java.desktop/java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.desktop/java.awt.EventQueue.access$500(Unknown Source)
        at java.desktop/java.awt.EventQueue$3.run(Unknown Source)
        at java.desktop/java.awt.EventQueue$3.run(Unknown Source)
        at java.base/java.security.AccessController.doPrivileged(Native Method)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
        at java.desktop/java.awt.EventQueue$4.run(Unknown Source)

我对 3x3 板尺寸使用了相同的 MCTS 代码，它不会崩溃并快速返回竞争动作。但是当我尝试将其用于 15x15 的棋盘尺寸时，游戏在 1235 次迭代后崩溃，并给出了上述错误。

我想我已经通过不允许在 1235 次迭代后扩展任何节点来处理问题的症状。这最终确实会返回一个竞争性的举动，尽管这需要很长时间才能发生。

对我来说，根本原因是我尝试创建的树的大小，因为相同的代码适用于 3x3 板，但不适用于 15x15 板;包含所有节点对象的树的大小太大了。因此，这只是这种方法的问题，而不是我的编码。

我确实认为我可以尝试：在 x 次迭代之后，如果一个节点被访问了 y 次但获胜分数低于 z，则删除该节点。我的想法是，如果经过 x 次迭代，并且被访问了 y 次，但仍然获胜分数较低，那么这个节点很可能占用了树中不必要的空间，因此可以删除。

我的问题是：

有没有更好的方法可以让我的程序返回移动而不是崩溃，而不仅仅是减少扩展次数，也不必实现上述检查？（即使最好的举动需要很长时间才能计算出来）。

以下是我一些未经编辑的代码：

已编辑** MCTS扩展功能：

public MCTSNode Expand(BoardGame game){
    MCTSNode child = new MCTSNode(game);
    for(int k = 0;k<this.gameState[0].length;k++){
      for(int l = 0;l<this.gameState[1].length;l++){
        child.gameState[k][l] = this.gameState[k][l];
      }
    }
    Random r = new Random();
    int possibleMoveSelected = r.nextInt(getPossibleMovesList());
    int row = getPossibleMoveX(possibleMoveSelected);
    int col = getPossibleMoveY(possibleMoveSelected);
    if(this.currentPlayer==2){
      child.gameState[row][col] = 2;
      child.moveMadeRow = row;
      child.moveMadeCol = col;
      child.currentPlayer = 1;
      child.setPossibleMoves();
      child.possibleMoves.size();
    }
    else{
      child.gameState[row][col] = 1;
      child.moveMadeRow = row;
      child.moveMadeCol = col;
      child.currentPlayer = 2;
      child.setPossibleMoves();
      child.possibleMoves.size();
    }
    childrenNode.add(child);
    child.parentNode = this;
    this.removePossibleMove(possibleMoveSelected);
    this.possibleMoves.trimToSize();
    return this;
}

MCTSPlayer功能：

public class MctsPlayer {

  private static int maxIterations;

  public MctsPlayer(int i){
    maxIterations = i;
  }


  public static String getBestMove(BoardGame game){
    MCTSNode root = new MCTSNode(game);
    root.getBoardState(game);
    root.setPossibleMoves();
    for(int iteration = 0; iteration < maxIterations; iteration++){
      MCTSNode initialNode = selectInitialNode(root);
      if(initialNode.getPossibleMovesList()>0){
        initialNode.Expand(game);
      }
      MCTSNode nodeSelected = initialNode;
      if(nodeSelected.childrenLeft() == true){
        nodeSelected = initialNode.getRNDChild();
      }
      nodeSelected.Simulate();
    }

    MCTSNode best = root.getMostVisitNode();
    System.out.println("This is the selected node's best move for the row: "+best.getMoveMadeRow());
    System.out.println("This is the selected node's best move for the col: "+best.getMoveMadeCol());
    best.printNodeInfo();
  }

新包含在下面**

选择初始节点函数（将继续，直到可能的移动列表大小为 == 到 0）：

public static MCTSNode selectInitialNode(MCTSNode node){
    MCTSNode initialNode = node;
    while (initialNode.getPossibleMovesSize()==0&&initialNode.checkForEmptySpace()==true){
      initialNode = initialNode.Select();

“+initialNode.childrenList（））; System.out.println（“剩余的节点可能移动： ”+initialNode.getPossibleMovesSize（））; } 返回 initialNode; }

选择功能：

public MCTSNode Select(){
  double maxUCT = Integer.MIN_VALUE;
  MCTSNode Node = this;
  if(this.possibleMoves.size()>0){
    return Node;
      }
  else{
    for(int i = 0;i<childrenNode.size();i++){
      double UCTValue = getUCTValue(getChildren(i));
      if(UCTValue > maxUCT){
        Node = getChildren(i);
        maxUCT = UCTValue;
      }
    }
    return Node;
  }

private double getUCTValue(MCTSNode childNode) {
        double UCTValue;
        if (childNode.getVisitCount() >= 1) {
          UCTValue = (Math.sqrt(2)*
              (Math.sqrt(Math.log(childNode.getParent().getVisitCount()* 1.0) / childNode.getVisitCount())) + (1.0 *childNode.getWinCount() / childNode.getVisitCount()* 1.0));
        } else {
            UCTValue = Double.MAX_VALUE;
        }
        return UCTValue;
  }

childrenLeft 函数：

public boolean childrenLeft(){
  return childrenNode.size()>0;
}