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 an array-based stack.

DSA C

void push(int stack[], int *top, int value, int max_size) {
    if (*top < max_size - 1) {
        stack[++(*top)] = [1];
    }
}

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

Avalue

Btop

Cmax_size

Dstack

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable instead of the value to push.

Not incrementing the top index before assignment.

The value to push onto the stack is assigned to the next position in the array.

2fill in blank

medium

Complete the code to create a new node for a linked list stack push operation.

DSA C

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

Node* push(Node* top, int value) {
    Node* new_node = (Node*)malloc(sizeof(Node));
    if (new_node == NULL) return top;
    new_node->data = [1];
    new_node->next = top;
    return new_node;
}

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

Avalue

Btop

CNULL

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning the pointer top instead of the value.

Forgetting to assign the data field.

The new node's data field should be set to the value being pushed onto the stack.

3fill in blank

hard

Fix the error in the array stack pop function to return the popped value correctly.

DSA C

int pop(int stack[], int *top) {
    if (*top == -1) {
        return -1; // Stack empty
    }
    return stack[[1]];
}

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

A*top

B(*top)++

C--(*top)

D(*top)--

Attempts:

3 left

💡 Hint

Common Mistakes

Not decrementing top (e.g., using just `*top`).

Using pre-decrement `--(*top)` which accesses the wrong element.

Use the post-decrement operator to return the value at the current top and then decrement the top index.

4fill in blank

hard

Fill both blanks to check if the linked list stack is empty and return the top element's data.

DSA C

int peek(Node* top) {
    if (top == [1]) {
        return -1; // Stack empty
    }
    return top->[2];
}

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

ANULL

B0

Cdata

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Checking top against 0 instead of NULL.

Returning the next pointer instead of data.

Check if top is NULL to see if stack is empty, then return the data field of the top node.

5fill in blank

hard

Fill all three blanks to implement a function that returns the current size of an array stack.

DSA C

int size(int *top) {
    return [1] + [2];
}

// Usage example:
// int current_size = size(&[3]);

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

A*top

B1

Ctop

Dstack

Attempts:

3 left

💡 Hint

Common Mistakes

Returning top without adding 1.

Passing the wrong variable to the function.

The size is *top + 1 because top starts at -1 when empty. Pass &top where top is the top index variable.

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. It requires less pointer management

B. Accessing elements by index is faster

C. Memory usage is always less

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

Solution

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

   A linked list stack can grow or shrink dynamically because nodes are allocated as needed.

2. Step 2: Compare with array stack size limits

   An array stack has a fixed size or needs resizing, which is costly and limits capacity.

3. Final Answer:

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

4. Quick Check:

   Dynamic size = Linked list stack advantage [OK]

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

Common Mistakes:

• Thinking array stacks can grow without resizing
• Assuming linked lists use less memory always
• Confusing access speed advantages

2. Which syntax correctly declares a stack node for a linked list stack in C?

easy

A. typedef struct Node { int data; struct Node* next; } Node;

B. struct Node { int data; int next; };

C. typedef struct Node { int data; Node* next; } Node;

D. struct Node { int data; struct Node next; };

Solution

1. Step 1: Check correct pointer declaration

   The next pointer must be of type 'struct Node*' to point to the next node.

2. Step 2: Validate typedef usage

   typedef struct Node { int data; struct Node* next; } Node; correctly uses typedef and struct pointer syntax in C.

3. Final Answer:

   typedef struct Node { int data; struct Node* next; } Node; -> Option A

4. Quick Check:

   Correct pointer syntax = typedef struct Node { int data; struct Node* next; } Node; [OK]

Hint: Use 'struct Node* next;' for linked list pointers in C [OK]

Common Mistakes:

• Using 'Node* next;' without 'struct' in C
• Declaring next as int instead of pointer
• Missing typedef or incorrect struct syntax

3. What will be the output after pushing 10, 20, then 30 onto an empty linked list stack and then popping once?

medium

A. 20 -> 10 -> null

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

C. 10 -> null

D. 20 -> null

Solution

1. Step 1: Push 10, 20, 30 onto stack

   Stack after pushes: top = 30, then 20, then 10 at bottom.

2. Step 2: Pop once removes top (30)

   After pop, top is 20, next is 10, then null.

3. Final Answer:

   20 -> 10 -> null -> Option A

4. Quick Check:

   Pop removes top = 20 -> 10 [OK]

Hint: Pop removes last pushed item; list shows remaining stack [OK]

Common Mistakes:

• Confusing push order with pop order
• Listing stack bottom first
• Forgetting pop removes top element

4. Given this array stack code snippet, what is the error?

int stack[3];
int top = -1;
void push(int x) {
  if(top == 3) {
    printf("Stack Overflow\n");
    return;
  }
  stack[++top] = x;
}

medium

A. The push function does not increment top

B. The stack array size is too large

C. The overflow condition should be 'top == 2' instead of 'top == 3'

D. The stack should be declared as a pointer

Solution

1. Step 1: Check array size and top index limits

   Array size is 3, so valid indices are 0,1,2; top max should be 2.

2. Step 2: Analyze overflow condition

   Condition 'top == 3' allows top to go out of bounds; should be 'top == 2'.

3. Final Answer:

   The overflow condition should be 'top == 2' instead of 'top == 3' -> Option C

4. Quick Check:

   Array max index = 2, overflow check must match [OK]

Hint: Array index max = size-1; check overflow accordingly [OK]

Common Mistakes:

• Checking overflow with wrong index
• Assuming top starts at 0
• Confusing array size with max index

5. Which of the following is a disadvantage of using an array-based stack compared to a linked list stack in a system with limited memory fragmentation?

hard

A. Linked list stack has slower push and pop operations

B. Array stack requires contiguous memory, which may be unavailable

C. Array stack uses more memory per element due to pointers

D. Linked list stack cannot be resized dynamically

Solution

1. Step 1: Understand memory allocation for array stacks

   Array stacks need a continuous block of memory, which can be hard to find if memory is fragmented.

2. Step 2: Compare with linked list memory allocation

   Linked lists allocate nodes separately, so they handle fragmentation better.

3. Final Answer:

   Array stack requires contiguous memory, which may be unavailable -> Option B

4. Quick Check:

   Contiguous memory need = array stack disadvantage [OK]

Hint: Arrays need continuous memory; linked lists do not [OK]

Common Mistakes:

• Thinking linked lists are slower always
• Assuming arrays use more memory per element
• Believing linked lists cannot resize dynamically