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Building a tree recursively

Posted on 2004-04-13
Last Modified: 2013-11-18
I am doing a method to build a tree recursively. But i doubt it would work. Can someone help? I would like to supply this method with the root node, which contains a player's current coordinate in a game board. And then from there to continuously add children to the root node. Children are adjacent coordinates of the root node. I need to recursively build this tree until the depth is = 2. I am not sure if the int depth = 0 thing will overwrite itself in each recursive call or not. can someone check?

public GameTreeNode buildGameTree(GameTreeNode aNode)
             int i=0;
             int depth = 0;
             if (depth != 2)
                   int pCopy1[] = new int[aNode.player.length]; // cloning 4 copies of the root's coordinate
                   int pCopy2[] = new int[aNode.player.length];
                   int pCopy3[] = new int[aNode.player.length];
                   int pCopy4[] = new int[aNode.player.length];
                  System.arraycopy(aNode.player, 0, pCopy1, 0, aNode.player.length);  
                  System.arraycopy(aNode.player, 0, pCopy2, 0, aNode.player.length);
                  System.arraycopy(aNode.player, 0, pCopy3, 0, aNode.player.length);
                  System.arraycopy(aNode.player, 0, pCopy4, 0, aNode.player.length);
                  pCopy1[0]++;      // right hand path coordinate
                  pCopy2[0]--;      // left hand path coordinate
                  pCopy3[1]++;      // upper path coordinate
                  pCopy4[1]--;      // down path coordinate
                  GameTreeNode child1 = new GameTreeNode(pCopy1); // building 4 nodes a time
                  GameTreeNode child2 = new GameTreeNode(pCopy2);
                  GameTreeNode child3 = new GameTreeNode(pCopy3);
                  GameTreeNode child4 = new GameTreeNode(pCopy4);
                  aNode.addChild(child1);   // adding 4 nodes a time...
                  System.out.println("ADDING 4 childs");
Question by:jtcy
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LVL 86

Expert Comment

ID: 10813651
>>I am not sure if the int depth = 0 thing will overwrite itself in each recursive call or not

Yes it will. You should make it an instance variable
LVL 37

Assisted Solution

zzynx earned 250 total points
ID: 10813715
I won't comment your current code.

But I think a better (OO) approach would be that each TreeNode (knowing at what dept it is) adds its own children.

something like:

class GameTreeNode extends DefaultMutableTreeNode {

    private int myDepth = 0;
    public GameTreeNode(Object userObject, int depth) {
         myDepth = depth;

    private void addSubNodes() {
         if (myDepth==2)
         // add a subnode (it's constructor will take care of loading its children):
         add( new GameTreeNode(yourUserObject, myDepth+1) );

Author Comment

ID: 10813716
is this the good way of building a tree? I am not sure actually. I mean, considering its performance. Is it fast or slow?
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LVL 37

Expert Comment

ID: 10813813
>> You should make it an instance variable
CEHJ means,

          int depth

a member of the buildGameTree()'s class.


class YourClass {
      private int depth=0;

      public GameTreeNode buildGameTree(GameTreeNode aNode) {
           // int depth = 0;  // <<<< remove this line

>> is this the good way of building a tree?
cf. my previous comment (considering the OO design & maintainability)

>> considering its performance
I don't see a problem
Anyway, once you have to create the children.
LVL 85

Expert Comment

by:Mike Tomlinson
ID: 10817874
An alternative approach would be to pass the depth in to your buildGameTree()  function as one of the parameters.  When you pass in the root node, pass in the depth as zero.  Then increment your depth as you are in code and continue to make your recursive calls.


Accepted Solution

wll9111 earned 250 total points
ID: 10949509
public int minimax(GameState aState, String player, int depth,int alpha, int beta)
           if (target_level == depth)
                   return evaluate(aState);
                 Vector movements = makeMoves(aState);            // create all possible moves...
                     if (player.equals("min"))
                                   for (int i = 0; i<movements.size();i++)
                                          if (alpha<beta)
                                               GameState temp = (GameState)movements.get(i);
                                               int score = minimax(temp,"max",depth+1,alpha,beta);
                                               if (score < beta)
                                                      beta = score;
                                         return beta;
                 if (player.equals("max"))
                               for (int j=0;j<movements.size();j++)
                                      if (alpha<beta)
                                           GameState temp2 = (GameState)movements.get(j);
                                           int score2 = minimax(temp2,"min",depth+1,alpha,beta);
                                           if (score2>alpha)
                                                  alpha = score2;
                                                  bestScore = alpha;
                                  return alpha;
              return bestScore;

Expert Comment

ID: 10949540
 public static void main(String[] args) throws java.io.IOException
            FileReader inFile = new FileReader(args[0]);                        // creating two copies of the input file...
            FileReader inFile2 = new FileReader(args[0]);
            Yylex lexer = new Yylex(inFile);                                          // creating a lexer...
            Parser parser = new Parser(lexer);                                          // creating a parser...
            parser.debugParser = true;                                                // debugging tools set off by default...
            parser.printAST = true;
            // get the start symbol...
                 // here we create a listing file...

LVL 37

Expert Comment

ID: 10949668
Hi, wll9111, sure you put your comments in the right Q?
LVL 37

Expert Comment

ID: 10949769
Strange things are happening here.
16 days wihtout further comments.
And now a comment that at first sight (I'll stay moderate) doesn't have any link to the Q is accepted within minutes.

jtcy, could you please comment on this?

Author Comment

ID: 10949913
sorry, that;s my course mate. I told him to join here post the solution for me.
LVL 37

Expert Comment

ID: 10950012
>> I told him to join here post the solution for me
Is that really the solution to your Q "how to build a tree recursively"?
????  8-O

If you can explain that you certainly deserve a ton of points.

Author Comment

ID: 10950046
um...sort of, actually he posted the wrong topic but anyway I asked the question intentioned to how to implement the minimax tree recursively, so yeah.
LVL 37

Expert Comment

ID: 10950129
>> actually he posted the wrong topic
There's nothing against posting the right answer (or let it post by someone you know and even accept)
But accepting the wrong answer is not so nice for all the people who'll read this Q in the future...

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