Binary Tree Node Structure in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Binary Tree Node Creation

What is the output of the following JavaScript code that creates a simple binary tree node and prints its structure?

DSA Javascript

class TreeNode {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(10);
root.left = new TreeNode(5);
root.right = new TreeNode(15);

console.log(JSON.stringify(root));

A {"value":10,"left":{"value":5,"left":null,"right":null},"right":{"value":15,"left":null,"right":null}}

B {"value":10,"left":5,"right":15}

C {"value":10,"left":null,"right":null}

D SyntaxError: Unexpected token

💡 Hint

Think about how the TreeNode class stores left and right children as objects, not just values.

The TreeNode class creates nodes with value, left, and right properties. Left and right are either null or TreeNode objects. The JSON.stringify prints the full nested structure.

❓ Predict Output

intermediate

Value of Left Child Node

After running this code, what is the value of the left child node of the root?

DSA Javascript

function TreeNode(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}

const root = new TreeNode(20);
root.left = new TreeNode(10);
root.right = new TreeNode(30);

const leftValue = root.left.value;
console.log(leftValue);

A 10

B 20

C 30

D null

💡 Hint

Look at what value is assigned to root.left.

The left child node is created with value 10, so root.left.value is 10.

🔧 Debug

advanced

Identify the Error in Binary Tree Node Assignment

What error will this code produce when run?

DSA Javascript

class TreeNode {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(5);
root.left.value = 3;
console.log(root.left.value);

A undefined

B 3

C TypeError: Cannot set property 'value' of null

D SyntaxError

💡 Hint

Check if root.left is initialized before setting its value.

root.left is null initially, so trying to set root.left.value causes a TypeError.

❓ Predict Output

advanced

Output of Nested Binary Tree Node Structure

What is the output of this code that creates a nested binary tree and prints the root's right child's left child's value?

DSA Javascript

class TreeNode {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(1);
root.right = new TreeNode(2);
root.right.left = new TreeNode(3);

console.log(root.right.left.value);

A 1

B 3

C null

D 2

💡 Hint

Trace the path from root to right child, then to left child.

root.right.left is a TreeNode with value 3, so printing its value outputs 3.

🧠 Conceptual

expert

Number of Nodes in a Binary Tree

Given a binary tree node structure where each node has 'left' and 'right' pointers, what is the total number of nodes after executing this code?

DSA Javascript

class TreeNode {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(10);
root.left = new TreeNode(5);
root.right = new TreeNode(15);
root.left.left = new TreeNode(3);
root.left.right = new TreeNode(7);
root.right.right = new TreeNode(18);

A 4

B 5

C 7

D 6

💡 Hint

Count each node created including root and all children.

Nodes created: root(1), root.left(2), root.right(3), root.left.left(4), root.left.right(5), root.right.right(6). Total 6 nodes.