Remove Node from Binary Search Tree

I am working on Binary Search Tree for the first time and trying to remove a node from the Binary Search Tree.

However, everytime I remove it and then I use inOrder() or preOrder() to check if it's removed or not, it still shows up, which means I fail to remove that particular node.

This is my code:

public class BinaryTree<T extends Comparable<T>> {
    TreeNode<T> root;
    ArrayList<Integer> myArr = new ArrayList<Integer>();
    Random random;
}

public void add(T o) {
    if (root == null) {
        root = new TreeNode<T>(o);
    } else {
        root.insert(o);
    }
}

public TreeNode<T> deleteNode(TreeNode<T> root, int value) {
    if (root == null)
        return null;
    if (root.data > value) {
        root.left = deleteNode(root.left, value);
    } else if (root.data < value) {
        root.right = deleteNode(root.right, value);
    } else {
        // if nodeToBeDeleted have both children
        if (root.left != null && root.right != null) {
            TreeNode<T> temp = root;
            // Finding minimum element from right
            TreeNode<T> minNodeForRight = minimumElement(temp.right);
            // Replacing current node with minimum node from right subtree
            root.data = minNodeForRight.data;
            // Deleting minimum node from right now
            deleteNode(root.right, minNodeForRight.data);
        }
        // if nodeToBeDeleted has only left child
        else if (root.left != null) {
            root = root.left;
        }
        // if nodeToBeDeleted has only right child
        else if (root.right != null) {
            root = root.right;
        }
        // if nodeToBeDeleted do not have child (Leaf node)
        else
            root = null;
    }
    return root;
}

public TreeNode<T> minimumElement(TreeNode<T> root) {
    if (root.left == null){
        return root;
    } else {
        return minimumElement(root.left);
    }
}

public static void main(String[] args){
    BinaryTree<Integer> bst = new BinaryTree<Integer>();
    bst.add(20);
    bst.add(30);
    bst.add(40);
    bst.add(80);
    bst.add(1200);
    bst.inOrder();
    bst.deleteNode(bst.root, 80);
    bst.inOrder();
}

How to solve this problem?

1 answer

  • answered 2018-11-08 06:09 efex09

    Change following line

    // Deleting minimum node from right now
    deleteNode(root.right, minNodeForRight.data);
    

    To

    // Deleting minimum node from right now
    root.right = deleteNode(root.right, minNodeForRight.data);