CODEWITHSUNDEEP
javarecursionbinary-tree
KBusc
KBusc

Reputation: 663

Java binary tree add method over writes root

I am trying to write a binary tree and the add method is continually overwriting the root of the tree. I have two methods a recursive add method that takes in a String and a Node and then a regular add method that simply calls the recursive method. Any help would be greatly appreciated.

public   Node recAdd(String event , Node tNode ){
//tNode -> tree node         
  if (tNode == null){
  // Addition place found
    root = new Node(event); 
    System.out.println("added root");
  }
  else if (tNode.event.compareTo(event) <= 0){
   tNode.setLeft(recAdd(event, tNode.getLeft()));   
   // System.out.println("added left");// Add in left subtree
  }
  else{
    tNode.setRight(recAdd(event, tNode.getRight()));
    //   System.out.println("added right");
  }// Add in right subtree
  return tNode;
}

//////////////////////////////////////////////

public  void add(String event){
  if(root != null){
    System.out.println("The root currently is " + root.event );
   }
   recAdd(event , root);
}

And my node class is as follows

public class Node {
  Node left;
  Node  right;
  String event;

  Node(String event){
    this.event = event;
    this.left = null;
    this.right = null;  
  }

  public void setEvent(String event){
    this.event = event;
  } 
  public void setLeft(Node left){
    this.left = left;
  } 
  public void setRight(Node right){
    this.right = right;
  } 

  public  String getEvent(){
    return event;
  }

  public Node getLeft(){
    return left;
  }
  public Node getRight(){
    return right;
  }
}

Upvotes: 0

Views: 2797

Answers (2)

cyfur01
cyfur01

Reputation: 3302

What's happening is that you recursively search through the tree until you reach a node that hasn't been assigned yet (i.e., it is null). At this point, you are overwriting root rather than creating the new node.

For example:

        root
       /    \
    node     null <- You want to assign this node, not overwrite root
   /    \ 
 null   null

To do this:

public   Node recAdd(String event , Node tNode ){       
    if (tNode == null){
        tNode = new Node(event);  // <--- Don't overwrite root
    }
    else if (tNode.event.compareTo(event) <= 0){
        tNode.setLeft(recAdd(event, tNode.getLeft()));   
    }
    else{
        tNode.setRight(recAdd(event, tNode.getRight()));
    }
    return tNode;
}

You would also need to modify your add() function:

public  void add(String event){
    root = recAdd(event , root); // <-----Reassign root
}

Upvotes: 0

Chris Dargis
Chris Dargis

Reputation: 6043

You are replacing the root node whenever you find a spot to insert the current node:

public Node recAdd(String event, Node tNode) {
    //tNode -> tree node         
    if (tNode == null) {
      // Addition place found
      root = new Node(event);     // Problem is RIGHT HERE
      System.out.println("added root");
    }
  //...
}

Upvotes: 1

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