Push Using Linked List Node in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with given data.

DSA C++

Node* newNode = new Node([1]);

Drag options to blanks, or click blank then click option'

Anext

Bdata

Chead

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' instead of data when creating the node.

Passing 'head' instead of the data value.

Using NULL as data.

We create a new node by passing the data value to the Node constructor.

2fill in blank

medium

Complete the code to link the new node to the current head.

DSA C++

newNode->[1] = head;

Drag options to blanks, or click blank then click option'

Adata

Bprev

Cnext

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' instead of 'next' to link nodes.

Using 'prev' which is for doubly linked lists.

Using 'value' which is not a pointer.

The 'next' pointer of the new node should point to the current head node.

3fill in blank

hard

Fix the error in updating the head pointer to the new node.

DSA C++

head = [1];

Drag options to blanks, or click blank then click option'

AnewNode

Bhead->next

CnewNode->next

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to newNode->next which skips the new node.

Assigning head to head->next which moves head incorrectly.

Assigning head to NULL which empties the list.

The head should be updated to point to the new node after insertion.

4fill in blank

hard

Fill both blanks to complete the push function that adds a node at the front.

DSA C++

void push(Node*& head, int data) {
    Node* newNode = new Node([1]);
    newNode->[2] = head;
    head = newNode;
}

Drag options to blanks, or click blank then click option'

Adata

Bnext

Chead

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' as data value.

Using 'value' instead of 'next' pointer.

Swapping the order of assignments.

We create a new node with 'data' and link its 'next' to the current head.

5fill in blank

hard

Fill all three blanks to complete the push function with proper node creation and linking.

DSA C++

void push(Node*& head, int data) {
    Node* newNode = new Node([1]);
    newNode->[2] = [3];
    head = newNode;
}

Drag options to blanks, or click blank then click option'

Adata

Bnext

Chead

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' pointer which is not used in singly linked list.

Assigning 'head' before linking newNode.

Passing wrong variable to Node constructor.

Create new node with 'data', set its 'next' to current 'head', then update 'head'.

Practice

1. What does the push operation do in a linked list when using nodes?

easy

A. Deletes the entire linked list

B. Removes the last node from the list

C. Searches for a node with a specific value

D. Adds a new node at the beginning of the list

Solution

1. Step 1: Understand push operation in linked list

   The push operation inserts a new node at the start (head) of the linked list.

2. Step 2: Effect of push on list structure

   The new node becomes the head, and its next pointer points to the previous head node.

3. Final Answer:

   Adds a new node at the beginning of the list -> Option D

4. Quick Check:

   Push means insert at head = D [OK]

Hint: Push always adds node at the start (head) [OK]

Common Mistakes:

• Confusing push with pop (removal)
• Thinking push adds at the end
• Mixing push with search or delete

2. Which of the following is the correct syntax to create a new node and push it at the head in C++ linked list?

easy

A. Node* newNode = new Node(data); newNode->next = head; head = newNode;

B. Node newNode = Node(data); head = newNode.next;

C. newNode = Node(data); newNode.next = head; head = newNode;

D. Node* newNode = Node(data); head = newNode->next;

Solution

1. Step 1: Create new node dynamically

   Use new Node(data) to allocate memory and initialize node.

2. Step 2: Link new node to current head and update head

   Set newNode->next = head and then head = newNode to push at front.

3. Final Answer:

   Node* newNode = new Node(data); newNode->next = head; head = newNode; -> Option A

4. Quick Check:

   Dynamic allocation + pointer update = B [OK]

Hint: Use pointer and 'new' keyword to create and link node [OK]

Common Mistakes:

• Not using pointer (*) for new node
• Using dot (.) instead of arrow (->) for pointers
• Assigning head incorrectly

3. What will be the output linked list after executing this code?

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

Node* head = nullptr;

// Push 10
Node* newNode1 = new Node(10);
newNode1->next = head;
head = newNode1;

// Push 20
Node* newNode2 = new Node(20);
newNode2->next = head;
head = newNode2;

// Push 30
Node* newNode3 = new Node(30);
newNode3->next = head;
head = newNode3;

// Print list
Node* temp = head;
while(temp != nullptr) {
  std::cout << temp->data << " -> ";
  temp = temp->next;
}
std::cout << "null";

medium

A. 10 -> 20 -> 30 -> null

B. 30 -> 20 -> 10 -> null

C. 20 -> 30 -> 10 -> null

D. null

Solution

1. Step 1: Trace push operations

   First push 10: list is 10 -> null. Then push 20: list becomes 20 -> 10 -> null. Then push 30: list becomes 30 -> 20 -> 10 -> null.

2. Step 2: Print linked list

   Printing from head prints 30, then 20, then 10, then null.

3. Final Answer:

   30 -> 20 -> 10 -> null -> Option B

4. Quick Check:

   Push adds at head, last pushed is first = C [OK]

Hint: Last pushed node appears first in list [OK]

Common Mistakes:

• Assuming push adds at tail
• Mixing order of nodes
• Not updating head pointer correctly

4. Identify the error in this push function for a singly linked list:

void push(Node* head, int data) {
  Node* newNode = new Node(data);
  newNode->next = head;
  head = newNode;
}

medium

A. head is passed by value, so original list head is not updated

B. newNode is not allocated dynamically

C. newNode->next should be nullptr

D. Function should return void* instead of void

Solution

1. Step 1: Analyze parameter passing

   head is passed by value, so changes inside function do not affect original head pointer.

2. Step 2: Effect on linked list

   Assigning head = newNode only changes local copy; original list head remains unchanged.

3. Final Answer:

   head is passed by value, so original list head is not updated -> Option A

4. Quick Check:

   Pass pointer by reference or pointer to pointer [OK]

Hint: Pass head by reference or pointer to update original [OK]

Common Mistakes:

• Ignoring parameter passing method
• Not returning new head if passed by value
• Incorrect pointer usage

5. You want to implement a stack using a singly linked list with push operation. Which approach correctly maintains the stack's LIFO order?

hard

A. Push new nodes at the tail and update head pointer

B. Push new nodes at the tail of the linked list without tail pointer

C. Push new nodes at the head of the linked list

D. Insert new nodes randomly in the list

Solution

1. Step 1: Understand stack LIFO behavior

   Stack requires last-in, first-out order, so newest element must be accessed first.

2. Step 2: Push at head maintains LIFO

   Adding new nodes at head means newest node is always at front, enabling O(1) push and pop.

3. Step 3: Problems with tail insertion

   Inserting at tail without tail pointer is inefficient and does not maintain LIFO easily.

4. Final Answer:

   Push new nodes at the head of the linked list -> Option C

5. Quick Check:

   Stack push = insert at head = A [OK]

Hint: Stack push uses head insertion for O(1) LIFO [OK]

Common Mistakes:

• Pushing at tail without tail pointer (slow)
• Not maintaining LIFO order
• Inserting nodes randomly