二进制搜索树查找父节点

Question

i have this code and i want to know if this gives the exact parent of the left and right child after insertion,so i made this code but I am not sure if this could get the right parent.

public Node insert(int x, Node t) 
{
    if (t == null)
    {
        t = new Node(x, null, null);
    }
    else if (x < t.iData) {
        t.leftChild = insert(x, t.leftChild);
        t.parent.leftChild = t ; 
    }
    else if (x > t.iData) {
        t.rightChild = insert(x, t.rightChild);
        t.parent.rightChild = t ;
    }
    else ;  // Duplicate; do nothing
    return t;
}


public class Node {
    int iData ;
    Node leftChild ;
    Node rightChild ;
    Node parent;
    public Node(int iData)
    {
        this.iData = iData;
        leftChild=null;
        rightChild=null;
        parent=null;

    }
    public Node(int iData, Node leftChild, Node rightChild) {
        this.iData = iData;
        this.leftChild = leftChild;
        this.rightChild = rightChild;
        parent=null;
    }
}

Answer 1

The only problem that I see with your code is that when you try to add the parent of a newly added node. Consider these two lines ::

t.leftChild = insert(x, t.leftChild);
t.parent.leftChild = t;

Consider you are on a node say A whose iData is less than x and t.leftChild is NULL so, you recur in the insert function. In the recursive call since the second argument of the insert is NULL you create a new node and return it, which is then saved in the leftChild pointer of A (when you return). After you have returned from the recursive call, you perform t.parent.leftChild = t; which actually means, that you go the parent of A and modify the leftChild of the parent of A , and NOT the parent of the newly added node, which does not make sense to what to you are trying to do. So, the correct way to do it, would be changing the lines where you assign the parent node to this::

t.leftChild.parent = t; //when x < iData
// Now you are changing the parent of the leftChild of A

and similarly,

t.rightChild.parent = t; //when x > iData

But, consider that the tree is very large, and you have to insert a node, for inserting one node and assigning a parent value to it, following the code you have written you will be reassigning the parent values of nodes to something that has already been assigned before and you are simply wasting time there. A more appropriate way to the same would be ::

void insert(Node t, int x) {
    if(t == NULL) { // In case the root of the tree is NULL
        t = new Node(x);
    } else if(t.iData == x) {
        return; // Do nothing
    } else if(t.iData > x) { //left branch
        if(t.leftChild == NULL) { // This is the place where you have to insert node
            t.leftChild = new Node(x);
            t.leftChild.parent = t;
        } else { // You have more branches to traverse
            insert(t.leftChild, x); 
            // Here you do not unnecessarily assign parent values again.
        }
    } else { //t.iData < x
        if(t.rightChild== NULL) { // This is the place where you have to insert node
            t.rightChild= new Node(x);
            t.rightChild.parent = t;
        } else { // You have more branches to traverse
            insert(t.rightChild, x); 
            // Here you do not unnecessarily assign parent values again,
            // when you return from recursion.
        }
    }
}