Binary search tree using recursion ?

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I am creating a Binary search tree using recursion , but there is this one thing I am not getting my head around. I have given my Insertion code below, What I am not getting is , inside the insert() method below , why do we have to use root==insertNode(root,data) ? I mean I know it'll invoke the next method , but why do we have to use the "root=" ? I tried removing it which gives me error.
Please explain.

Java

public void insert(int data){
        root=insertNode(root,data);
    }


    private Node insertNode(Node root,int data){

        Node newNode = new Node(data);

        if (root==null){
            root=newNode;
            return root;
        }

        if (data < root.data){
            root.left=insertNode(root.left,data);
        }else {
            root.right=insertNode(root.right,data);
        }
        return root;
    }

What I have tried:

I tried google but didnt got the required answer

Posted 2-Sep-20 3:31am

Deepesh mhatre

Updated 2-Sep-20 20:32pm

v3

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Sandeep Mewara 2-Sep-20 9:50am

which line you are talking of. Your code says single '=' and your question talks about '==' (in context of insert method). Where is the confusion?

[no name] 2-Sep-20 11:35am

root=insertNode(root,data);
THE 2 LINE

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CPallini · Answer 1 · 2020-09-02T03:48:00

Solution 1

Quote:
why do we have to use root==insertNode(root,data) ?

You have to use

Java

root=insertNode(root,data); // note the single '='

because the parent of newly inserted node needs to be updated with the reference to the newly inserted node itself.

Posted 2-Sep-20 3:48am

CPallini

Sandeep Mewara · Answer 2 · 2020-09-02T20:32:00

Quote:
root=insertNode(root,data); //THE 2 LINE

You were right on that part. It's not mandatory to put root = and should be okay to just call insert here and ignore the return. Its on you what you want to do with the returned value from a method - use it or ignore.

In your above code, I couldn't locate root defined. Hope that is not related to your issue.

See, I tried the same and it works as expected:

Java

public class JavaFiddle
{
    public static void main(String[] args)
    {
    
      insert(10);
      System.out.println("HelloWorld!");
    }
    
    public static void insert(int data){
        Node root=new Node(1);
        //root=insertNode(root,data);
        insertNode(root,data);
    }
    
    
    private static Node insertNode(Node root,int data){
    
        Node newNode = new Node(data);
    
        if (root==null){
            root=newNode;
            return root;
        }
    
        if (data < root.data){
            root.left=insertNode(root.left,data);
        }else {
            root.right=insertNode(root.right,data);
        }
        return root;
    }
    
    public static class Node
    {
        Node left;
        int data;
        Node right;
        
        Node(int data)
        {
            this.data = data;
        }
    }
}

Binary search tree using recursion ?

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