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#

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

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

Atop

BstackArray

Ccapacity

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

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

Not incrementing 'top' before assignment.

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

2fill in blank

medium

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

DSA C#

public int Pop() {
    if (head == null) throw new InvalidOperationException("Stack is empty");
    int value = head.data;
    head = [1];
    return value;
}

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

Ahead.data

Bhead.next

Cnull

Dhead.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Setting 'head' to null which empties the stack incorrectly.

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

After popping, we move the head pointer to the next node in the linked list.

3fill in blank

hard

Fix the error in the array stack resize method to double the capacity.

DSA C#

private void Resize() {
    int newCapacity = capacity * [1];
    int[] newArray = new int[newCapacity];
    Array.Copy(stackArray, newArray, capacity);
    stackArray = newArray;
    capacity = newCapacity;
}

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

A2

B1

Ccapacity

D0.5

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying by 1 which does not change capacity.

Multiplying by 0.5 which halves capacity.

Doubling the capacity means multiplying by 2.

4fill in blank

hard

Fill both blanks to create a linked list node and push it onto the stack.

DSA C#

public void Push(int value) {
    Node newNode = new Node([1]);
    newNode.next = [2];
    head = newNode;
}

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

Avalue

Bhead

Cnull

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Setting newNode.next to null which breaks the stack chain.

Passing 'head' as the value instead of the actual value.

We create a new node with the value and link it to the current head before updating head.

5fill in blank

hard

Fill all three blanks to check if the array stack is full and resize if needed before pushing.

DSA C#

public void Push(int value) {
    if (top == [1] - 1) {
        [2]();
    }
    stackArray[++[3]] = value;
}

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

Acapacity

BResize

Ctop

DPush

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'top == top - 1' which is always false.

Calling 'Push' recursively causing infinite loop.

We check if 'top' reached 'capacity - 1', call 'Resize()', then increment 'top' before assignment.

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 can grow dynamically without a fixed size limit

C. Memory usage is always less

D. It uses less pointer overhead

Solution

1. Step 1: Understand stack growth in arrays

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

2. Step 2: Understand linked list flexibility

   Linked lists can grow dynamically by adding nodes, so the stack size is limited only by memory.

3. Final Answer:

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

4. Quick Check:

   Linked list stacks grow dynamically = B [OK]

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

Common Mistakes:

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

2. Which of the following is the correct way to declare an array-based stack of integers with size 10 in C#?

easy

A. int[] stack = new int[10];

B. int stack = new int[10];

C. int[] stack = int[10];

D. int stack[] = new int(10);

Solution

1. Step 1: Recall C# array declaration syntax

   In C#, arrays are declared with type[], then new type[size].

2. Step 2: Check each option

   int[] stack = new int[10]; matches correct syntax: int[] stack = new int[10]; others have syntax errors.

3. Final Answer:

   int[] stack = new int[10]; -> Option A

4. Quick Check:

   C# array syntax = D [OK]

Hint: Use type[] name = new type[size]; for arrays in C# [OK]

Common Mistakes:

• Missing [] after type
• Using parentheses instead of brackets for size
• Declaring array without new keyword

3. Consider this C# code using a linked list stack implementation:

StackNode top = null;
// Push 10
StackNode node1 = new StackNode(10);
node1.Next = top;
top = node1;
// Push 20
StackNode node2 = new StackNode(20);
node2.Next = top;
top = node2;
// Pop
int popped = top.Data;
top = top.Next;
Console.WriteLine(popped);

What is the output?

medium

A. NullReferenceException

B. 10

C. 20

D. 0

Solution

1. Step 1: Trace push operations

   First push 10: top points to node with 10. Then push 20: top points to node with 20, next points to 10.

2. Step 2: Trace pop operation

   Pop reads top.Data = 20, then top moves to next node (10).

3. Final Answer:

   20 -> Option C

4. Quick Check:

   Last pushed is first popped = A [OK]

Hint: Last pushed node is popped first in linked list stack [OK]

Common Mistakes:

• Confusing push order and pop order
• Assuming pop returns bottom element
• Forgetting to update top pointer

4. The following C# code attempts to push an element onto an array-based stack but causes a runtime error:

int[] stack = new int[2];
int top = 2;
stack[top] = 5;

What is the main issue causing the error?

medium

A. NullReferenceException due to uninitialized array

B. Stack overflow exception because stack is full

C. Syntax error in array declaration

D. Array index out of bounds because 'top' equals array size

Solution

1. Step 1: Understand array indexing in C#

   Array indices go from 0 to length-1, so valid indices are 0 and 1 for size 2.

2. Step 2: Check 'top' value usage

   Variable 'top' is 2, which is outside valid index range, causing index out of bounds error.

3. Final Answer:

   Array index out of bounds because 'top' equals array size -> Option D

4. Quick Check:

   Index must be less than array size = A [OK]

Hint: Array indices start at 0, max index is size-1 [OK]

Common Mistakes:

• Confusing stack overflow with index error
• Assuming array indices start at 1
• Ignoring that array is initialized properly

5. You need to implement a stack that will store a very large number of elements, but memory is limited and resizing arrays is costly. Which implementation is better and why?

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

hard

A. Linked list stack, because it uses memory only as needed and avoids resizing overhead

B. Array stack, because arrays always use less memory than linked lists

C. Array stack, because resizing is fast and memory is unlimited

D. Linked list stack, because it allows random access to elements

Solution

1. Step 1: Consider memory usage and resizing cost

   Array stacks need resizing which copies all elements, costly in time and memory.

2. Step 2: Consider linked list memory behavior

   Linked lists allocate memory per element, no resizing needed, so better for large unknown sizes with limited memory.

3. Final Answer:

   Linked list stack, because it uses memory only as needed and avoids resizing overhead -> Option A

4. Quick Check:

   Linked list avoids resizing overhead = C [OK]

Hint: Linked list stacks avoid costly resizing for large data [OK]

Common Mistakes:

• Assuming arrays always use less memory
• Ignoring resizing cost in arrays
• Thinking linked lists allow random access