Stack Implementation Using Linked List in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the Node structure for the stack.

DSA C++

struct Node {
    int data;
    [1] *next;
};

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

AElement

BStack

CList

DNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong type name for the pointer.

Forgetting the asterisk '*' for pointer declaration.

The pointer to the next node must be of type 'Node*' to link nodes in the stack.

2fill in blank

medium

Complete the code to initialize the top pointer of the stack to empty.

DSA C++

Node* top = [1];

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

Anullptr

B0

CNULL

DNULLPTR

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'NULL' instead of 'nullptr'.

Using integer 0 instead of a pointer null value.

In modern C++, 'nullptr' is used to represent a null pointer safely.

3fill in blank

hard

Fix the error in the push function to correctly link the new node.

DSA C++

void push(int value) {
    Node* newNode = new Node();
    newNode->data = value;
    newNode->next = [1];
    top = newNode;
}

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

Avalue

BnewNode

Ctop

Dnullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to nullptr loses the rest of the stack.

Setting next to newNode causes self-loop.

The new node's next pointer should point to the current top node before updating top.

4fill in blank

hard

Fill both blanks to correctly implement the pop function that removes the top element.

DSA C++

int pop() {
    if (top == nullptr) {
        return -1; // Stack empty
    }
    Node* temp = top;
    int poppedValue = top->data;
    top = [1];
    delete [2];
    return poppedValue;
}

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

Atop->next

Btemp

Ctop

Dnullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Deleting top before updating it causes dangling pointer.

Not updating top leads to incorrect stack state.

Update top to the next node, then delete the old top stored in temp.

5fill in blank

hard

Fill all three blanks to implement a function that prints all stack elements from top to bottom.

DSA C++

void printStack() {
    Node* current = [1];
    while (current != [2]) {
        std::cout << current->[3] << " -> ";
        current = current->next;
    }
    std::cout << "null" << std::endl;
}

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

Atop

Bnullptr

Cdata

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for traversal.

Looping incorrectly causing infinite loop or crash.

Start from top, loop until nullptr, print data of each node.

Practice

1. What is the main advantage of implementing a stack using a linked list instead of an array?

easy

A. It uses less memory than an array

B. The stack can grow dynamically without a fixed size limit

C. It allows random access to elements

D. It is easier to sort the stack elements

Solution

1. Step 1: Understand stack size limitation in arrays

   Arrays have fixed size, so stack implemented with arrays has a maximum capacity.

2. Step 2: Linked list dynamic size property

   Linked lists can grow or shrink dynamically by adding or removing nodes, so stack size is not fixed.

3. Final Answer:

   The stack can grow dynamically without a fixed size limit -> Option B

4. Quick Check:

   Linked list stack size = dynamic growth [OK]

Hint: Linked list stacks grow dynamically, arrays have fixed size [OK]

Common Mistakes:

• Thinking linked list uses less memory always
• Assuming stack allows random access
• Confusing sorting with stack operations

2. Which of the following is the correct syntax to create a new node in a linked list stack in C++?

easy

A. Node* newNode = new Node(value);

B. Node newNode = Node(value);

C. Node newNode = new Node(value);

D. Node* newNode = Node(value);

Solution

1. Step 1: Understand dynamic memory allocation in C++

   To create a node dynamically, use 'new' keyword and pointer type.

2. Step 2: Check syntax correctness

   Node* newNode = new Node(value); uses pointer and 'new' correctly: Node* newNode = new Node(value);

3. Final Answer:

   Node* newNode = new Node(value); -> Option A

4. Quick Check:

   Dynamic node creation = new + pointer [OK]

Hint: Use 'new' with pointer to create nodes dynamically [OK]

Common Mistakes:

• Omitting pointer (*) when using new
• Using stack allocation instead of dynamic
• Assigning new object to non-pointer variable

3. What will be the output after executing the following code snippet for a stack implemented using linked list?

Stack s;
s.push(10);
s.push(20);
s.push(30);
s.pop();
s.push(40);
s.display();

Assuming display prints elements from top to bottom.

medium

A. 40 -> 30 -> 20 -> 10 -> null

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

C. 20 -> 10 -> null

D. 40 -> 20 -> 10 -> null

Solution

1. Step 1: Trace push and pop operations

   Push 10, stack: 10; push 20, stack: 20->10; push 30, stack: 30->20->10; pop removes 30, stack: 20->10; push 40, stack: 40->20->10.

2. Step 2: Determine display output

   Display prints from top to bottom: 40 -> 20 -> 10 -> null.

3. Final Answer:

   40 -> 20 -> 10 -> null -> Option D

4. Quick Check:

   Stack after ops = 40->20->10 [OK]

Hint: Track push/pop stepwise to find top element [OK]

Common Mistakes:

• Forgetting pop removes top element
• Assuming push adds at bottom
• Mixing order of elements in display

4. Identify the error in the following pop function of a linked list stack:

int pop() {
  if (top == NULL) {
    cout << "Stack Underflow";
    return -1;
  }
  int val = top->data;
  delete top;
  top = top->next;
  return val;
}

medium

A. Returning -1 on empty stack is incorrect

B. Missing check for stack overflow

C. Accessing top->next after deleting top causes undefined behavior

D. Not updating top pointer after pop

Solution

1. Step 1: Analyze order of operations in pop

   Code deletes top node before accessing top->next, which is unsafe.

2. Step 2: Identify correct order

   Must save top->next in a temp pointer before deleting top, then update top.

3. Final Answer:

   Accessing top->next after deleting top causes undefined behavior -> Option C

4. Quick Check:

   Delete before next access = error [OK]

Hint: Save next pointer before deleting current node [OK]

Common Mistakes:

• Deleting node before updating pointer
• Ignoring stack underflow check
• Returning wrong values on empty stack

5. You want to implement a function to reverse a stack implemented using a linked list without using extra data structures. Which approach is correct?

hard

A. Use recursion to pop all elements and push them back in reverse order

B. Traverse the linked list and swap data of nodes pairwise

C. Create a new linked list and copy elements in reverse order

D. Use a queue to reorder elements and then push back to stack

Solution

1. Step 1: Understand constraints

   No extra data structures allowed, so cannot use queue or new list.

2. Step 2: Use recursion to reverse stack

   Recursion can pop all elements, then push them back in reverse order naturally.

3. Step 3: Why other options fail

   Swapping data pairwise does not reverse entire stack; copying needs extra list; queue is extra structure.

4. Final Answer:

   Use recursion to pop all elements and push them back in reverse order -> Option A

5. Quick Check:

   Recursion reverses stack without extra structures [OK]

Hint: Recursion can reverse stack without extra memory [OK]

Common Mistakes:

• Using extra data structures despite constraints
• Trying to swap data instead of nodes
• Not understanding recursion stack behavior