BST删除方法不会删除插入的第一个节点

Question

I can't figure this out... I can insert and sort items with no issue, I can delete nodes past the first insert, but on the special case that I'm trying to delete the first node inserted to start the tree, it doesn't do anything.

I'm not understanding why this issue is happening, any help to figure out the logic is appreciated.

Watered down version of my code the replicates the problem. https://pastebin.com/hxcqpG1U

Here is my delete method:

    public void delete(KeyComp key) {
    delete(_root, key);
}

private Node delete(Node root, KeyComp key) {
    //TO-DO: DELETE AN ITEM IN THE TABLE, GIVEN THE KEY

    //empty tree
    if (root == null)
        return root;

    if (key.keyCompareTo(root.data) < 0)
        root.left = delete(root.left, key);
    else if (key.keyCompareTo(root.data) > 0)
        root.right = delete(root.right, key);

    else
    {
        // node with only one child or no child
        if (root.left == null)
            return root.right;
        else if (root.right == null)
            return root.left;

        // node with two children: Get the inorder successor (smallest
        // in the right subtree)
        root.data = getMin(root.right).data;

        // Delete the inorder successor
        root.right = delete(root.right, root.data);
    }

    return root;
}

Answer 1

Assuming your tree does no balancing, the first node inserted will be the root node of the tree. Since your delete method operates by updating the in-tree references to point around the deleted node, trying to delete the root node won't do anything unless you also update the pointer to the root node.

It's hard to tell from the code you've provided, but it seems likely that you need something like:

public void delete(KeyComp key) {
    _root = delete(_root, key);
}