Create a Binary Tree Manually in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a binary tree?

A binary tree is a structure where each node has up to two children called left and right. It looks like a family tree with each parent having at most two kids.

beginner

How do you create a node in a binary tree manually?

You create a node by making an object with a value and two pointers: left and right. Both pointers start as null because the node has no children yet.

beginner

What does the 'left' pointer in a binary tree node represent?

The 'left' pointer points to the left child node. If there is no left child, it is null.

beginner

What is the root node in a binary tree?

The root node is the top node of the tree. It has no parent and is the starting point to access all other nodes.

beginner

How do you link nodes to form a binary tree manually?

You assign the left and right pointers of a node to other nodes to connect them. This builds the tree structure step by step.

What is the maximum number of children a node can have in a binary tree?

A One

B Unlimited

C Three

D Two

In a binary tree, each node can have at most two children: left and right.

What is the initial value of left and right pointers when creating a new node manually?

A Undefined

B Null

C Zero

D Empty string

Left and right pointers start as null because the node has no children yet.

Which node is called the root in a binary tree?

A The top node with no parent

B Any leaf node

C The bottom-most node

D A node with two children

The root node is the top node with no parent and is the starting point of the tree.

How do you connect nodes to form a binary tree manually?

A By deleting nodes

B By copying node values

C By assigning left and right pointers

D By swapping nodes

You connect nodes by assigning the left and right pointers to other nodes.

If a node has no left child, what is the left pointer value?

A Null

B Zero

C Undefined

D Empty string

If there is no left child, the left pointer is null.

Explain how to create a simple binary tree manually with three nodes.

Think about making three boxes and linking them with arrows for left and right.

Describe the role of left and right pointers in a binary tree node.

Imagine each node as a person holding hands with up to two children.

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