Binary Tree Node Structure in DSA Typescript - Execution Trace

Concept Flow - Binary Tree Node Structure

Create new node

↓

Assign data value

↓

Set left child pointer to null

↓

Set right child pointer to null

↓

Node ready for use in tree

This flow shows how a binary tree node is created with data and two child pointers initialized to null.

Execution Sample

DSA Typescript

class TreeNode {
  data: number;
  left: TreeNode | null;
  right: TreeNode | null;

  constructor(data: number) {
    this.data = data;
    this.left = null;
    this.right = null;
  }
}

This code defines a binary tree node with data and two child pointers initialized to null.

Execution Table

Step	Operation	Node Data	Left Pointer	Right Pointer	Visual State
1	Create node with data=10	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
2	Assign data=10	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
3	Set left pointer to null	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
4	Set right pointer to null	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
5	Node ready for use	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘

💡 Node created with data and both child pointers set to null, ready to be linked in a binary tree.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
data	undefined	10	10	10	10	10
left	undefined	null	null	null	null	null
right	undefined	null	null	null	null	null

Key Moments - 2 Insights

Why are left and right pointers set to null initially?

Because in the execution_table rows 3 and 4, we see left and right pointers assigned null to indicate no children yet. This prevents errors when traversing the tree.

Is the data assigned before or after setting pointers?

Data is assigned first (step 2) before pointers are set (steps 3 and 4), as shown in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of the right pointer after step 3?

A undefined

B 10

C null

D Not set yet

💡 Hint

Check the 'Right Pointer' column in row for step 3 in execution_table.

At which step is the node considered ready for use in the tree?

A Step 3

B Step 5

C Step 4

D Step 2

💡 Hint

Look at the 'Operation' column and 'Visual State' in execution_table for the final step.

If we skip setting left pointer to null, what would be the left pointer value after step 3?

A undefined

B data value

C null

D Error

💡 Hint

Refer to variable_tracker for 'left' variable changes and default initialization.

Concept Snapshot

Binary Tree Node Structure:
- Each node has data, left, and right pointers.
- Data holds the value.
- Left and right pointers start as null (no children).
- Nodes link to form the binary tree.
- Initialize pointers to null to avoid traversal errors.

Full Transcript

This concept shows how to create a binary tree node in TypeScript. The node has three parts: data, left pointer, and right pointer. We first create the node and assign the data value. Then we set the left and right pointers to null, meaning the node has no children yet. This setup is essential before linking nodes to form a binary tree. The execution table traces each step, showing the node's data and pointers. The variable tracker confirms how data and pointers change from undefined to their final values. Key moments clarify why pointers start as null and the order of assignments. The visual quiz tests understanding of pointer values at different steps. The snapshot summarizes the node structure and initialization rules.

Practice

1. What does a typical binary tree node contain in its structure?

easy

A. Only a value and a pointer to the next node

B. A value, a left child node, and a right child node

C. A value and multiple child nodes in a list

D. Only a value without any child nodes

Solution

1. Step 1: Understand binary tree node components

   A binary tree node typically stores a value and references to two children: left and right.

2. Step 2: Compare options with definition

   A value, a left child node, and a right child node correctly lists value, left child, and right child. Others describe linked list or general tree nodes.

3. Final Answer:

   A value, a left child node, and a right child node -> Option B

4. Quick Check:

   Binary tree node = value + left + right [OK]

Hint: Binary tree nodes always have two child pointers [OK]

Common Mistakes:

• Confusing binary tree node with linked list node
• Thinking nodes have multiple children like general trees
• Ignoring child pointers in node structure

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

easy

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

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

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

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

Solution

1. Step 1: Check property types and initialization

   class Node { value: number; left: Node | null; right: Node | null; constructor(value: number) { this.value = value; this.left = null; this.right = null; } } correctly declares left and right as Node or null and initializes them to null in constructor.

2. Step 2: Verify constructor parameters and assignments

   class Node { value: number; left: Node | null; right: Node | null; constructor(value: number) { this.value = value; this.left = null; this.right = null; } } constructor takes value and sets left and right to null, matching typical binary tree node setup.

3. Final Answer:

   Correct TypeScript class with nullable children and proper constructor -> Option C

4. Quick Check:

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

Hint: Child nodes must allow null to represent empty branches [OK]

Common Mistakes:

• Not initializing left and right to null
• Using undefined instead of null for children
• Missing constructor parameter for value

3. Given the following TypeScript code, 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);
console.log(root.left?.value);

medium

A. 5

B. undefined

C. null

D. 10

Solution

1. Step 1: Analyze node assignments

   root.left is assigned a new Node with value 5, so root.left is not null.

2. Step 2: Understand optional chaining and output

   Using root.left?.value safely accesses value of left node, which is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   root.left.value = 5 [OK]

Hint: Optional chaining returns value if node exists, else undefined [OK]

Common Mistakes:

• Confusing null and undefined outputs
• Assuming root.left is null by default
• Misreading optional chaining operator

4. Identify the error in this TypeScript binary tree node class and fix it:

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

medium

A. left and right should allow null type (Node | null)

B. Constructor should not assign null to left and right

C. value should be optional in constructor

D. Class should not have a constructor

Solution

1. Step 1: Check property types vs assigned values

   left and right are typed as Node but assigned null, causing type error.

2. Step 2: Fix type declarations

   Change left and right types to Node | null to allow null assignment.

3. Final Answer:

   left and right should allow null type (Node | null) -> Option A

4. Quick Check:

   Nullable children fix type error [OK]

Hint: Child nodes must be nullable if assigned null [OK]

Common Mistakes:

• Not updating types when assigning null
• Removing constructor unnecessarily
• Making value optional without reason

5. How would you modify the binary tree node class to include a parent pointer, and what is the impact on tree traversal?

hard

A. No changes needed; parent pointer is implicit in left and right

B. Add a parent property of type number; no impact on traversal

C. Add a parent property as an array of nodes; allows multiple parents

D. Add a parent property of type Node | null; allows upward traversal from child to parent

Solution

1. Step 1: Understand parent pointer addition

   Adding a parent property of type Node | null stores reference to parent node.

2. Step 2: Impact on traversal

   This allows traversing upwards from child to parent, enabling bidirectional navigation.

3. Final Answer:

   Add a parent property of type Node | null; allows upward traversal from child to parent -> Option D

4. Quick Check:

   Parent pointer enables upward traversal [OK]

Hint: Parent pointer lets you move up the tree easily [OK]

Common Mistakes:

• Using wrong type for parent pointer
• Assuming parent pointer exists by default
• Confusing parent pointer with multiple parents