Question

I am trying to write my own binary tree and I have problems with insertion. The values in tree are duplicated. I have inner static class Node with “Node right,left and int value” fields and outer class BinaryTree with one field – Node root.

The code of insertion:

public void insert(int number) {
    if (root.isEmpty())
        root.value = number;
    else {
        Node node = root;
        insert(number, node);
    }
}

private void insert(int number, Node node) {
    if (number < node.value && node.left != null) {
        node = node.left;
        insert(number, node);
    } else {
        if (node.left == null)
            node.left = new Node(null, null, number);
    }

    if (number > node.value && node.right != null) {
        node = node.right;
        insert(number, node);
    } else {
        if (node.right == null)
            node.right = new Node(null, null, number);
    }
}

What i am doing wrong?

Answer 1

Suppose you have a node called X as root.
You are inserting some number

if (number < node.value && node.left != null) {
    node = node.left; // NODE IS NOW Y
    insert(number, node);
} 

Now it goes in the next if statement

if (number > node.value && node.right != null) {
    node = node.right;
    insert(number, node);
} else {
    if (node.right == null)
        node.right = new Node(null, null, number);
}

node is equal to Y now and has no children. So node.right==null. So the number is reinserted as Y’s right child.

SO there exists a copy of the number. Solve it using return.

private void insert(int number, Node node) {
    if (number < node.value && node.left != null) {
        node = node.left;
        insert(number, node);
        return;
    } 
    else {
        if (node.left == null)
            node.left = new Node(null, null, number);
        return;
    }

    if (number > node.value && node.right != null) {
        node = node.right;
        insert(number, node);
        return;
    }
    else {
        if (node.right == null)
            node.right = new Node(null, null, number);
        return;
    }
}