Removing a node from a binary search tree in Java?

Question

I've been given a binary search tree, and as part of what I've been tasked to do, I need to implement a remove() method on both my set and node class.

Right now however, my JUnit tests are failing to remove items correctly. Code as follows:

BSTSet

public boolean remove(E item) {     
    if (this.contains(item)) {
        this.root.remove(item);
        this.count--;
        return true;
    }   

    return false;
}

BSTNode

public BSTNode<E>remove(E item) {
    if (item.equals(this.value)) {
        return this.replacementSubtreeFromChildren(this.left, this.right);
    }

    if (item.compareTo(this.value) < 0) {
        this.left = this.left.remove(item);
    } else {
        this.right = this.right.remove(item);
    }

    // there was no need to replace the receiver node
    return this;  
}

where replacementSubtreeFromChildren is:

private BSTNode<E> replacementSubtreeFromChildren(BSTNode<E> left, BSTNode<E> right) {
    if (left == null && right == null) {
        return null;
    }

    if (left != null && right == null) {
        return left;
    }

    if (right != null && left == null) {
        return right;
    }

    this.getLeftmostNode().value = this.right.getLeftmostNode().value;      
    this.value = this.getLeftmostNode().value;      
    return this;
}

I'd prefer an indirect answer if possible. I'd like to try and figure this out myself. Can anyone provide some pointers as to what's going wrong here?

Answer 1

Wouldn't say this is an answer but I can't comment with my rep. Posting how the node is implemented would help.

if your tree is being visualized as an array [10, 5, 12] such that 5, is the left node of 10, and 12 is the right node. if you called .remove(10). At the end of your ReplacementSubtreeFromChildren method you would have a tree that looked like this [12, 12, 12]. Because you're setting 5, to 12, then 10 to (what was the 5 value) 12.