Problems in binary tree traversal

Question

I am trying to implement a binary search tree with In order traversal. I am trying to print a series of numbers after each other to test it. It seems that it is sorting well, however it is printing dublicate numbers sometimes. Look at relevant pieces of my code:

Tree class and Methods:

 public class Tree {
Node root;

public Tree(){
root = null;
}


public Node add(Node n, int value){
if(n== null){
    n= new Node(value);
}else if(value < n.getValue()){
    n.addLeftNode(add(n.getLeft(),value));
}else if(value > n.getValue()){
    n.addRightNode(add(n.getRight(),value));
}

return n;
}

public static Node traverse(Node n){

Node result = new Node();

if(n != null){


    if(n.getLeft() != null){

        result = traverse(n.getLeft()); 
        System.out.println(result.getValue());                
    }

        result = n;
        System.out.println(result.getValue());      


    if(n.getRight() != null){     

        result = traverse(n.getRight());
        System.out.println(result.getValue());

    }

}
return result;
}
}

This is what it's printing out:

---

0 0 1 1 3 4 4 5 6 7 7 8 10 11 12 12 12 15 15 15 15 15 15 15 16 18 18 20 21 22 22 22 22 23 27 28 28 28 29 34 35 43 43 43 43 43 43 43 44 45 45 55 56 59 66 75 75 75 75 75 75 76 76 76 78 88 89 89 90 90 90 98 98

Any clues? I'm guessing it's something with the traversal. Tried debugging it however I still couldn't find the issue. As you can see Nos are sorted at least.

Answer 1

When you traverse left or right, the call into traverse will print the left/right node. You don't have to print left and right separately.

if(n != null){
    if(n.getLeft() != null){
        result = traverse(n.getLeft()); 
        // System.out.println(result.getValue());                
    }

    result = n;
    System.out.println(result.getValue()); // This prints the left and right via recursion into traverse(...)

    if(n.getRight() != null){     
        result = traverse(n.getRight());
        // System.out.println(result.getValue());
    }
}

Answer 2

Traverse method should be:

void traverse(Node n) {
    if(n == null)
        return;

    traverse(n.getLeft());
    System.out.println(n.getValue());
    traverse(n.getRight());
}