Stack Using Linked List vs Array Stack Trade-offs in DSA C++ - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the array-based stack.

DSA C++

void push(int value) {
    if (top < capacity - 1) {
        stackArray[++[1]] = value;
    }
}

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

Atop

Bcapacity

Cvalue

DstackArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'capacity' instead of 'top' to index the array.

Assigning value before incrementing top.

We increment the 'top' index before assigning the new value to the array position.

2fill in blank

medium

Complete the code to pop an element from the linked list stack.

DSA C++

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

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

Adata

Bprev

Cnext

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' which is incorrect for singly linked list.

Not updating head pointer.

To pop, we move the head pointer to the next node in the linked list.

3fill in blank

hard

Fix the error in the array stack's isFull() method.

DSA C++

bool isFull() {
    return top [1] capacity - 1;
}

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

A==

B>

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' which gives wrong full condition.

Using '>' which is invalid for this check.

The stack is full when 'top' equals 'capacity - 1'.

4fill in blank

hard

Fill the blank to correctly check if the linked list stack is empty.

DSA C++

bool isEmpty() {
    return head [1] nullptr;
}

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

A!=

B==

C&&

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which means not empty.

The stack is empty if head == nullptr.

5fill in blank

hard

Fill all three blanks to correctly populate a map with array stack elements greater than 10, using index as key.

DSA C++

auto filtered = std::map<int, int>{};
for (int i = 0; i < size; ++i) {
    if (stackArray[i] [3] 10) {
        filtered[[1]] = [2];
    }
}

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

Ai

BstackArray[i]

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for filtering.

Swapping key and value positions.

The code maps index 'i' to stackArray[i] only if stackArray[i] is greater than 10.

Practice

1. Which of the following is a key advantage of using a linked list to implement a stack compared to using an array?

easy

A. Accessing elements by index is faster.

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

C. Memory usage is always less than an array.

D. It uses less pointer memory.

Solution

1. Step 1: Understand stack size behavior in linked list

   A linked list stack can grow dynamically because nodes are created as needed without a fixed size.

2. Step 2: Compare with array stack size limits

   An array stack has a fixed size or requires resizing, which is costly. Linked list avoids this limitation.

3. Final Answer:

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

4. Quick Check:

   Dynamic size = Linked list advantage [OK]

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

Common Mistakes:

• Thinking arrays always use less memory
• Confusing access speed advantages
• Assuming linked lists use less pointer memory

2. Which of the following is the correct way to declare a stack using an array in C++?

easy

A. int stack[10]; int top = -1;

B. int stack; int top = 0;

C. int stack[]; int top = -1;

D. int stack(10); int top = -1;

Solution

1. Step 1: Check array declaration syntax

   In C++, arrays are declared with size inside square brackets, e.g., int stack[10];

2. Step 2: Check top initialization

   Top is initialized to -1 to indicate empty stack.

3. Final Answer:

   int stack[10]; int top = -1; -> Option A

4. Quick Check:

   Correct array syntax and top init = C [OK]

Hint: Array size in [] brackets; top starts at -1 [OK]

Common Mistakes:

• Using parentheses instead of brackets for array
• Not initializing top correctly
• Declaring array without size

3. Consider the following code snippet implementing a stack push operation using a linked list:

struct Node {
  int data;
  Node* next;
};

Node* top = nullptr;

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

push(10);
push(20);
push(30);

What will be the order of elements from top to bottom after these pushes?

medium

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

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

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

D. 30 -> 10 -> 20 -> null

Solution

1. Step 1: Trace push operations on linked list stack

   Each push adds new node at the top, so last pushed is on top.

2. Step 2: Order after pushes

   push(10) -> top=10; push(20) -> top=20->10; push(30) -> top=30->20->10

3. Final Answer:

   30 -> 20 -> 10 -> null -> Option C

4. Quick Check:

   Last in first out = 30 on top [OK]

Hint: Last pushed is always on top in linked list stack [OK]

Common Mistakes:

• Assuming order is 10->20->30
• Confusing push with append at end
• Ignoring pointer update order

4. The following code attempts to pop an element from an array-based stack but has a bug:

int stack[5];
int top = -1;

void pop() {
  if (top == 0) {
    cout << "Stack Underflow" << endl;
    return;
  }
  top--;
}

What is the bug in this pop function?

medium

A. It should print "Stack Overflow" instead of "Stack Underflow".

B. It should increment top instead of decrementing.

C. The stack array size is too small.

D. It should check if top == -1 for underflow, not top == 0.

Solution

1. Step 1: Understand stack underflow condition

   Underflow occurs when stack is empty, which is when top == -1.

2. Step 2: Check condition in code

   Code checks top == 0, which is wrong; top == 0 means one element is present.

3. Final Answer:

   It should check if top == -1 for underflow, not top == 0. -> Option D

4. Quick Check:

   Empty stack top = -1, check must match [OK]

Hint: Empty stack top is -1, check underflow with top == -1 [OK]

Common Mistakes:

• Checking top == 0 instead of -1
• Confusing overflow and underflow messages
• Incorrectly incrementing top on pop

5. You want to implement a stack that can handle millions of push and pop operations without worrying about maximum size. Which implementation is better and why?

1. Array-based stack with dynamic resizing
2. Linked list-based stack

hard

A. Linked list stack is better because it grows dynamically without resizing overhead.

B. Array stack is better because it uses less memory per element.

C. Array stack is better because dynamic resizing is always faster than linked list allocation.

D. Linked list stack is worse because it cannot grow beyond initial size.

Solution

1. Step 1: Consider dynamic resizing cost in array stack

   Array stack needs to resize and copy elements when full, which is costly for millions of operations.

2. Step 2: Consider linked list stack growth

   Linked list stack allocates nodes on demand, no resizing needed, so it handles large operations smoothly.

3. Final Answer:

   Linked list stack is better because it grows dynamically without resizing overhead. -> Option A

4. Quick Check:

   Dynamic growth without resizing = Linked list advantage [OK]

Hint: Linked list avoids resizing overhead for large stacks [OK]

Common Mistakes:

• Assuming array resizing is always faster
• Ignoring memory overhead of pointers
• Thinking linked list has fixed size