Binary Tree Node Structure in DSA C++ - 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 linking in tree

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

Execution Sample

DSA C++

struct Node {
  int data;
  Node* left;
  Node* right;
  Node(int val) : data(val), left(nullptr), right(nullptr) {}
};

Defines a binary tree node with an integer data and pointers to left and right children 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	Left pointer set to null	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
3	Right pointer set to null	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘
4	Node ready for linking	10	null	null	┌────────┐ │ data:10│ │ left:∅ │ │ right:∅│ └────────┘

💡 Node created with data 10 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	Final
data	undefined	10	10	10	10
left	undefined	null	null	null	null
right	undefined	null	null	null	null

Key Moments - 2 Insights

Why are left and right pointers set to null initially?

Because in the execution_table rows 2 and 3, both pointers are set to null to indicate the node has no children yet.

What does the visual state represent in each step?

It shows the node's data and the current state of its left and right pointers, which remain null until linked.

Visual Quiz - 3 Questions

Look at the execution_table at step 1, what is the value of the node's data?

A null

B 10

C undefined

D 0

💡 Hint

Check the 'Node Data' column in execution_table row with Step 1.

At which step are the left and right pointers both set to null?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Left Pointer' and 'Right Pointer' columns in execution_table rows.

If the right pointer was not set to null, what would the visual state show at step 3?

A right:∅

B right:undefined

C right:some garbage value

D right:null

💡 Hint

Pointers not initialized usually contain garbage values in memory before assignment.

Concept Snapshot

Binary Tree Node Structure:
- Each node holds data and two pointers: left and right.
- Pointers start as null (no children).
- Node created with constructor initializing data and pointers.
- Ready to link nodes to form a tree.

Full Transcript

This concept shows how to create a binary tree node in C++. The node has an integer data field and two pointers for left and right children. When a node is created, its data is set to the given value, and both pointers are set to null, meaning it has no children yet. The visual state shows the node as a box with data and pointers labeled. This node can then be linked to other nodes to build a binary tree.

Practice

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

easy

A. A data value and pointers to left and right child nodes

B. Only a data value without any pointers

C. Pointers to parent and sibling nodes only

D. A data value and a pointer to the next node in a list

Solution

1. Step 1: Understand binary tree node components

   A binary tree node stores a data value and has two pointers: one to the left child and one to the right child.

2. Step 2: Compare options with definition

   A data value and pointers to left and right child nodes correctly describes this structure. Other options miss pointers or mention unrelated pointers.

3. Final Answer:

   A data value and pointers to left and right child nodes -> Option A

4. Quick Check:

   Binary tree node = data + left + right pointers [OK]

Hint: Remember: binary tree nodes have two child pointers [OK]

Common Mistakes:

• Thinking nodes have only one pointer
• Confusing with linked list node structure
• Assuming parent pointer is always present

2. Which of the following is the correct syntax to define a binary tree node struct in C++?

easy

A. struct Node { int data; Node* left; Node* right; };

B. struct Node { int data; Node left; Node right; };

C. struct Node { int data; Node& left; Node& right; };

D. struct Node { int data; Node left*; Node right*; };

Solution

1. Step 1: Check pointer syntax in struct

   In C++, pointers are declared with '*', so left and right children must be pointers: Node* left; Node* right;

2. Step 2: Validate each option

   struct Node { int data; Node* left; Node* right; }; uses correct pointer syntax. struct Node { int data; Node left; Node right; }; uses objects (causes infinite recursion). struct Node { int data; Node& left; Node& right; }; uses references incorrectly. struct Node { int data; Node left*; Node right*; }; has invalid pointer syntax.

3. Final Answer:

   struct Node { int data; Node* left; Node* right; }; -> Option A

4. Quick Check:

   Pointer syntax = Node* left/right [OK]

Hint: Pointers use * after type, not before variable name [OK]

Common Mistakes:

• Using objects instead of pointers for children
• Using references (&) for child nodes
• Incorrect pointer syntax like 'left*'

3. What will be the output of the following code snippet?

struct Node {
  int data;
  Node* left;
  Node* right;
  Node(int val) : data(val), left(nullptr), right(nullptr) {}
};

int main() {
  Node* root = new Node(10);
  root->left = new Node(5);
  root->right = new Node(15);
  std::cout << root->left->data << " " << root->right->data << std::endl;
  return 0;
}

medium

A. Compilation error

B. 5 15

C. 5 10

D. 10 15

Solution

1. Step 1: Understand node creation and assignments

   Root node has data 10. Left child is assigned a node with data 5. Right child is assigned a node with data 15.

2. Step 2: Trace the output statement

   Output prints root->left->data (5) and root->right->data (15) separated by space.

3. Final Answer:

   5 15 -> Option B

4. Quick Check:

   Left child = 5, Right child = 15 [OK]

Hint: Follow pointer assignments to print child node data [OK]

Common Mistakes:

• Printing root data instead of children
• Confusing left and right child values
• Forgetting to initialize children

4. Identify the error in the following binary tree node struct and fix it:

struct Node {
  int data;
  Node left;
  Node right;
  Node(int val) : data(val) {}
};

medium

A. Remove constructor and use public members only

B. Add default constructor to initialize data

C. Change 'int data;' to 'int* data;'

D. Change 'Node left;' and 'Node right;' to 'Node* left;' and 'Node* right;'

Solution

1. Step 1: Identify the problem with member declarations

   Declaring 'Node left;' and 'Node right;' causes infinite recursion because each Node contains two Nodes inside it.

2. Step 2: Fix by using pointers for children

   Change to 'Node* left;' and 'Node* right;' to hold addresses of child nodes, avoiding infinite size.

3. Final Answer:

   Change 'Node left;' and 'Node right;' to 'Node* left;' and 'Node* right;' -> Option D

4. Quick Check:

   Child nodes must be pointers to avoid infinite recursion [OK]

Hint: Child nodes must be pointers, not objects [OK]

Common Mistakes:

• Using objects for children causing infinite size
• Ignoring pointer usage in tree nodes
• Trying to fix with constructors only

5. You want to create a binary tree node struct that also stores a pointer to its parent node. Which of the following is the correct way to define it?

hard

A. struct Node { int data; Node left; Node right; Node parent; Node(int val) : data(val) {} };

B. struct Node { int data; Node* left; Node* right; int* parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(nullptr) {} };

C. struct Node { int data; Node* left; Node* right; Node* parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(nullptr) {} };

D. struct Node { int data; Node* left; Node* right; Node& parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(*this) {} };

Solution

1. Step 1: Understand parent pointer type

   The parent pointer must be of type 'Node*' to point to another node or nullptr if no parent.

2. Step 2: Check constructor initialization

   Constructor initializes data and sets left, right, and parent pointers to nullptr correctly.

3. Step 3: Validate options

   struct Node { int data; Node* left; Node* right; Node* parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(nullptr) {} }; correctly uses pointers for children and parent. struct Node { int data; Node left; Node right; Node parent; Node(int val) : data(val) {} }; uses objects causing recursion. struct Node { int data; Node* left; Node* right; int* parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(nullptr) {} }; wrongly uses 'int*' for parent. struct Node { int data; Node* left; Node* right; Node& parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(*this) {} }; uses reference incorrectly and initializes parent to self.

4. Final Answer:

   struct Node { int data; Node* left; Node* right; Node* parent; Node(int val) : data(val), left(nullptr), right(nullptr), parent(nullptr) {} }; -> Option C

5. Quick Check:

   Parent pointer = Node* parent [OK]

Hint: Parent pointer must be Node* and initialized to nullptr [OK]

Common Mistakes:

• Using object or reference for parent pointer
• Incorrect pointer type for parent
• Initializing parent pointer incorrectly