Create a Binary Tree Manually in DSA Typescript - 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 branches splitting into two.

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: one for the left child and one for the right child. Both children can be empty (null) if no child exists.

beginner

What does the root node represent in a binary tree?

The root node is the top node of the tree. It is the starting point from where you can reach all other nodes by following left and right children.

intermediate

In TypeScript, how can you define a simple binary tree node type?

You can define it as a type or interface with a value of any type and two optional children nodes: left and right, which can be null or another node.

beginner

Why is it useful to create a binary tree manually?

Creating a binary tree manually helps understand how nodes connect and how trees grow. It is the base for learning tree traversal and other tree operations.

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

A Unlimited

B Three

C One

D Two

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

Which node is the starting point of a binary tree?

A Root node

B Leaf node

C Child node

D Sibling node

The root node is the top node and starting point of a binary tree.

In TypeScript, what type can represent a missing child in a binary tree node?

A null

B 0

C undefined

D empty string

We use null to show that a child node does not exist.

What does a binary tree node usually contain?

A Only a value

B Only two children

C Value and two children

D Value and three children

A binary tree node contains a value and pointers to left and right children.

Why create a binary tree manually?

A To sort numbers automatically

B To understand node connections

C To create a linked list

D To avoid learning trees

Manual creation helps understand how nodes connect and how trees work.

Explain how to create a binary tree manually using nodes with left and right children.

Think about how each node connects to two others or none.

Describe the role of the root node in a binary tree and how other nodes relate to it.

Imagine the root as the tree trunk from which branches grow.

Practice

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

easy

A. To avoid using classes or objects

B. To automatically sort data without coding

C. To understand how nodes connect and form the tree structure

D. To create a linked list instead of a tree

Solution

1. Step 1: Understand binary tree structure

   A binary tree consists of nodes where each node has at most two children, left and right.

2. Step 2: Purpose of manual creation

   Manually creating a binary tree helps visualize and understand how nodes connect to form the tree.

3. Final Answer:

   To understand how nodes connect and form the tree structure -> Option C

4. Quick Check:

   Manual creation = Understand tree structure [OK]

Hint: Manual creation helps visualize node connections [OK]

Common Mistakes:

• Thinking it automatically sorts data
• Confusing binary tree with linked list
• Assuming no objects or classes are needed

2. Which of the following is the correct way to define a binary tree node class in TypeScript?

easy

A. class Node { value: number; left: Node | null; right: Node | null; constructor(value: number) { this.value = value; this.left = null; this.right = null; } }

B. class Node { value: number; left: number; right: number; constructor(value: number) { this.value = value; this.left = 0; this.right = 0; } }

C. class Node { value: number; left: Node; right: Node; constructor(value: number) { this.value = value; } }

D. class Node { value: number; left: any; right: any; constructor() { this.value = 0; } }

Solution

1. Step 1: Check node properties and types

   A binary tree node should have a value and left/right children which can be nodes or null.

2. Step 2: Verify constructor initialization

   Constructor must initialize value and set left and right to null initially.

3. Final Answer:

   class Node { value: number; left: Node | null; right: Node | null; constructor(value: number) { this.value = value; this.left = null; this.right = null; } } -> Option A

4. Quick Check:

   Node class with nullable children = class Node { value: number; left: Node | null; right: Node | null; constructor(value: number) { this.value = value; this.left = null; this.right = null; } } [OK]

Hint: Children must be Node or null, initialized in constructor [OK]

Common Mistakes:

• Using number type for left/right instead of Node or null
• Not initializing left and right to null
• Omitting constructor parameters

3. Given the following TypeScript code to create a binary tree manually, what will be the output of console.log(root.left?.value)?

class Node {
  value: number;
  left: Node | null;
  right: Node | null;
  constructor(value: number) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

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

medium

A. 5

B. 10

C. 15

D. undefined

Solution

1. Step 1: Understand tree structure from code

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

2. Step 2: Access left child's value

   root.left?.value accesses left node's value safely, which is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   root.left.value = 5 [OK]

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

Common Mistakes:

• Confusing root value with left child value
• Expecting right child value instead
• Not using optional chaining and getting error

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

class Node {
  value: number;
  left: Node | null;
  right: Node | null;
  constructor(value: number) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

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

medium

A. Missing constructor parameters in Node class

B. Using wrong class name for Node

C. Not initializing root.right

D. Assigning number 5 to root.left instead of a Node or null

Solution

1. Step 1: Check type of root.left assignment

   root.left is declared as Node or null, but assigned number 5 which is invalid.

2. Step 2: Confirm correct assignment type

   root.left should be assigned a Node instance or null, not a number.

3. Final Answer:

   Assigning number 5 to root.left instead of a Node or null -> Option D

4. Quick Check:

   Type mismatch in root.left assignment = Assigning number 5 to root.left instead of a Node or null [OK]

Hint: Children must be Node or null, not a number [OK]

Common Mistakes:

• Assigning primitive values to node children
• Ignoring type errors in assignments
• Assuming number can be assigned directly

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

hard

A. const root = new Node(20);
root.left = 10;
root.right = 30;
console.log(root.value, root.left, root.right);

B. const root = new Node(20);
root.left = new Node(10);
root.right = new Node(30);
console.log(root.value, root.left?.value, root.right?.value);

C. const root = new Node(20);
root.left = new Node(30);
root.right = new Node(10);
console.log(root.value, root.left?.value, root.right?.value);

D. const root = new Node(20);
root.left = null;
root.right = null;
console.log(root.left?.value, root.value, root.right?.value);

Solution

1. Step 1: Create root and children nodes correctly

   Root node with value 20, left child 10, right child 30 must be Node instances.

2. Step 2: Print values in order root, left, right

   console.log prints root.value, root.left?.value, root.right?.value which outputs 20 10 30.

3. Final Answer:

   const root = new Node(20); root.left = new Node(10); root.right = new Node(30); console.log(root.value, root.left?.value, root.right?.value); -> Option B

4. Quick Check:

   Correct node creation and print order = const root = new Node(20); root.left = new Node(10); root.right = new Node(30); console.log(root.value, root.left?.value, root.right?.value); [OK]

Hint: Create nodes with new, assign children as nodes, print values [OK]

Common Mistakes:

• Assigning numbers directly to children
• Swapping left and right child values
• Printing children before root or using null children