Create a Binary Tree Manually in DSA Javascript - Build from Scratch

Create a Binary Tree Manually

📖 Scenario: You are building a simple binary tree by manually creating nodes and linking them. This is like making a family tree by connecting parents and children step by step.

🎯 Goal: Create a binary tree by defining nodes as objects and linking them as left and right children. Then print the tree structure in a readable format.

📋 What You'll Learn

Create a node object with value, left, and right properties

Manually link nodes to form a binary tree

Write a function to print the tree nodes in pre-order traversal

Print the tree nodes in the correct order

💡 Why This Matters

🌍 Real World

Binary trees are used in many places like organizing data, searching quickly, and making decisions step-by-step.

💼 Career

Understanding how to build and traverse trees is important for software development, especially in areas like databases, file systems, and algorithms.

1

Create the root node

Create a variable called root that is an object with value set to 10, and left and right set to null.

DSA Javascript

// Your code here

Hint

Think of the root as the main node with no children yet.

2

Add left and right children to root

Create two variables called leftChild and rightChild. Set leftChild to an object with value 5 and null children. Set rightChild to an object with value 15 and null children. Then assign root.left to leftChild and root.right to rightChild.

DSA Javascript

const root = { value: 10, left: null, right: null };
// Your code here

Hint

Link the children to the root by assigning them to root.left and root.right.

3

Add a left child to the left child node

Create a variable called leftLeftChild as an object with value 3 and null children. Assign leftChild.left to leftLeftChild.

DSA Javascript

const root = { value: 10, left: null, right: null };
const leftChild = { value: 5, left: null, right: null };
const rightChild = { value: 15, left: null, right: null };
root.left = leftChild;
root.right = rightChild;
// Your code here

Hint

Link the new node as the left child of the leftChild node.

4

Print the tree nodes in pre-order

Write a function called printPreOrder that takes a node and prints its value, then recursively prints the left child, then the right child. Call printPreOrder(root) to print all nodes.

DSA Javascript

const root = { value: 10, left: null, right: null };
const leftChild = { value: 5, left: null, right: null };
const rightChild = { value: 15, left: null, right: null };
root.left = leftChild;
root.right = rightChild;
const leftLeftChild = { value: 3, left: null, right: null };
leftChild.left = leftLeftChild;

// Your code here

Hint

Pre-order means print current node, then left subtree, then right subtree.

Practice

1. What is the main purpose of creating a binary tree manually in JavaScript?

easy

A. To convert a string into an array

B. To automatically sort numbers in an array

C. To create a list of numbers without any hierarchy

D. To build a tree structure by linking nodes with left and right children

Solution

1. Step 1: Understand what a binary tree is

   A binary tree is a structure where each node has up to two children: left and right.

2. Step 2: Purpose of manual creation

   Manually creating a binary tree means linking nodes by setting their left and right child references.

3. Final Answer:

   To build a tree structure by linking nodes with left and right children -> Option D

4. Quick Check:

   Binary tree = linked nodes with left/right children [OK]

Hint: Binary tree nodes link left and right children manually [OK]

Common Mistakes:

• Thinking binary tree sorts data automatically
• Confusing binary tree with arrays or lists
• Assuming binary tree nodes have more than two children

2. Which of the following is the correct way to create a node object for a binary tree in JavaScript?

easy

A. const node = [5, null, null];

B. const node = (5, null, null);

C. const node = { value: 5, left: null, right: null };

D. const node = 5, left = null, right = null;

Solution

1. Step 1: Understand JavaScript object syntax

   Objects use curly braces with key-value pairs, e.g., { key: value }.

2. Step 2: Check each option

   const node = { value: 5, left: null, right: null }; correctly uses an object with keys value, left, right. Others use array, parentheses, or invalid syntax.

3. Final Answer:

   const node = { value: 5, left: null, right: null }; -> Option C

4. Quick Check:

   Node as object with keys = const node = { value: 5, left: null, right: null }; [OK]

Hint: Use curly braces for node objects with keys [OK]

Common Mistakes:

• Using arrays instead of objects for nodes
• Using parentheses instead of braces
• Trying to declare multiple variables without braces

3. What will be the output of the following code that manually creates a binary tree and prints the root node's left child's value?

const root = { value: 10, left: { value: 5, left: null, right: null }, right: { value: 15, left: null, right: null } };
console.log(root.left.value);

medium

A. 5

B. 15

C. 10

D. undefined

Solution

1. Step 1: Understand the tree structure

   Root node has value 10, left child with value 5, right child with value 15.

2. Step 2: Access root.left.value

   root.left points to node with value 5, so root.left.value is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   root.left.value = 5 [OK]

Hint: Access left child value with root.left.value [OK]

Common Mistakes:

• Confusing root value with left child value
• Accessing root.right.value instead
• Expecting undefined if not careful with null checks

4. Identify the error in the following code that tries to create a binary tree node manually:

const node = { value: 7, left: null, right: null };
node.left.value = 3;

medium

A. Cannot assign value to left because left is null

B. Syntax error in object declaration

C. Missing semicolon after node declaration

D. No error, code runs fine

Solution

1. Step 1: Analyze node.left value

   node.left is set to null, so it has no properties.

2. Step 2: Assigning to node.left.value

   Trying to assign node.left.value = 3 causes error because node.left is null, cannot set property on null.

3. Final Answer:

   Cannot assign value to left because left is null -> Option A

4. Quick Check:

   Assigning property on null causes error [OK]

Hint: Check if child node exists before assigning properties [OK]

Common Mistakes:

• Ignoring that null has no properties
• Assuming automatic node creation on assignment
• Thinking missing semicolon causes error here

5. You want to manually create a binary tree with root value 20, left child 10, and right child 30. Which code correctly creates this tree and prints the right child's value?

hard

A. const root = { value: 20, left: 10, right: 30 };
console.log(root.right);

B. const root = { value: 20, left: { value: 10, left: null, right: null }, right: { value: 30, left: null, right: null } };
console.log(root.right.value);

C. const root = { value: 20, left: { 10 }, right: { 30 } };
console.log(root.right.value);

D. const root = { value: 20, left: null, right: null };
root.left = { value: 10, left: null, right: null };
root.right = { value: 30, left: null, right: null };
console.log(root.right.value);

Solution

1. Step 1: Check tree node structure

   Each child must be an object with value, left, right keys or null.

2. Step 2: Evaluate each option

   const root = { value: 20, left: { value: 10, left: null, right: null }, right: { value: 30, left: null, right: null } }; console.log(root.right.value); correctly creates left and right child nodes as objects with proper keys. const root = { value: 20, left: 10, right: 30 }; console.log(root.right); uses numbers directly, not objects. const root = { value: 20, left: { 10 }, right: { 30 } }; console.log(root.right.value); uses invalid object syntax. const root = { value: 20, left: null, right: null }; root.left.value = 10; root.right.value = 30; console.log(root.right.value); tries to assign properties to null children causing error.

3. Final Answer:

   const root = { value: 20, left: { value: 10, left: null, right: null }, right: { value: 30, left: null, right: null } }; console.log(root.right.value); -> Option B

4. Quick Check:

   Proper node objects with children = const root = { value: 20, left: { value: 10, left: null, right: null }, right: { value: 30, left: null, right: null } }; console.log(root.right.value); [OK]

Hint: Children must be objects with value, left, right keys [OK]

Common Mistakes:

• Assigning numbers directly as children
• Using invalid object syntax for children
• Assigning properties to null children