Dynamic Stack Using Resizable Array in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the array that stores stack elements.

DSA C#

private int[] [1];

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

Aelements

BstackArray

CstackList

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that is not declared in the class.

Confusing the array name with the stack size variable.

The array that stores the stack elements is named 'stackArray' in this implementation.

2fill in blank

medium

Complete the code to double the size of the array when resizing.

DSA C#

int newSize = stackArray.Length [1] 2;

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

A/

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' which adds instead of doubling.

Using '/' which halves the size.

To double the size, multiply the current length by 2.

3fill in blank

hard

Fix the error in the Push method to add the new element correctly.

DSA C#

stackArray[[1]] = item;

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Acount - 1

B0

Ccount + 1

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using count - 1 which overwrites the last element.

Using count + 1 which skips an index.

The new item should be placed at the index equal to the current count before incrementing.

4fill in blank

hard

Fill both blanks to correctly resize and copy elements to the new array.

DSA C#

int[] newArray = new int[[1]];
Array.[2](stackArray, newArray, count);

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AnewSize

BCopyTo

CCopy

DClone

Attempts:

3 left

💡 Hint

Common Mistakes

Using CopyTo which is an instance method, not static.

Using Clone which creates a shallow copy but not to a new array.

Create new array with newSize and use Array.Copy to copy elements.

5fill in blank

hard

Fill all three blanks to correctly implement the Pop method.

DSA C#

if (count == 0) throw new InvalidOperationException("Stack is empty");
count [1];
int item = stackArray[[2]];
stackArray[[3]] = 0;
return item;

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A--

Bcount - 1

Ccount

Dcount + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count - 1' instead of 'count' for the index.

Not decrementing count before accessing the array.

Decrement count first, then get item at count, clear that index, and return the item.

Practice

1. What is the main advantage of using a dynamic stack with a resizable array over a fixed-size array stack?

easy

A. It can grow or shrink automatically as elements are pushed or popped.

B. It uses less memory than a fixed-size array stack.

C. It always has a fixed capacity to avoid resizing overhead.

D. It does not allow popping elements.

Solution

1. Step 1: Understand fixed-size array stack limitation

   A fixed-size array stack has a set capacity and cannot grow beyond it, causing overflow if exceeded.

2. Step 2: Understand dynamic stack advantage

   A dynamic stack resizes its array automatically when full, allowing more elements without overflow.

3. Final Answer:

   It can grow or shrink automatically as elements are pushed or popped. -> Option A

4. Quick Check:

   Dynamic resizing = automatic growth/shrink [OK]

Hint: Dynamic stacks resize arrays automatically when full [OK]

Common Mistakes:

• Thinking dynamic stack uses less memory always
• Believing dynamic stack has fixed capacity
• Confusing dynamic stack with linked list stack

2. Which of the following is the correct way to double the size of the internal array in a dynamic stack in C#?

easy

A. array = new int[array.Length * 2];

B. array.Length = array.Length * 2;

C. array = array.Concat(array).ToArray();

D. Array.Resize(ref array, array.Length * 2);

Solution

1. Step 1: Understand array resizing in C#

   Arrays in C# have fixed length; to resize, use Array.Resize(ref array, newSize) which copies old elements.

2. Step 2: Analyze options

   Array.Resize(ref array, array.Length * 2); uses Array.Resize correctly. array = new int[array.Length * 2]; creates a new array but loses old data. array.Length = array.Length * 2; is invalid syntax. array = array.Concat(array).ToArray(); uses LINQ but is inefficient and not typical for stack resizing.

3. Final Answer:

   Array.Resize(ref array, array.Length * 2); -> Option D

4. Quick Check:

   Array.Resize method resizes arrays properly [OK]

Hint: Use Array.Resize(ref array, newSize) to resize arrays in C# [OK]

Common Mistakes:

• Trying to set array.Length directly
• Creating new array without copying old data
• Using LINQ Concat for resizing inefficiently

3. Consider the following C# code for a dynamic stack using a resizable array:

DynamicStack stack = new DynamicStack();
stack.Push(10);
stack.Push(20);
stack.Push(30);
stack.Pop();
stack.Push(40);
stack.PrintStack();

What will be the printed output?

medium

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

B. 40 -> 20 -> 10 -> null

C. 20 -> 10 -> null

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

Solution

1. Step 1: Trace stack 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 printed output

   PrintStack prints from top to bottom ending with null: 40 -> 20 -> 10 -> null

3. Final Answer:

   40 -> 20 -> 10 -> null -> Option B

4. Quick Check:

   Stack top after operations = 40 [OK]

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

Common Mistakes:

• Forgetting pop removes top element
• Printing stack in wrong order
• Including popped elements in output

4. The following code snippet for a dynamic stack has a bug. What is the error?

public void Push(int item) {
  if (top == array.Length) {
    Array.Resize(ref array, array.Length * 2);
  }
  array[top] = item;
  top++;
}

medium

A. No bug; the code resizes and pushes correctly.

B. The top variable should be incremented before assigning the item.

C. The condition should be top == array.Length to resize, but top starts at 1 instead of 0.

D. The condition should be top == array.Length - 1 to resize.

Solution

1. Step 1: Analyze resizing condition

   top equals array.Length means array is full, so resizing is needed before adding new item.

2. Step 2: Check push logic

   Assign item at array[top], then increment top. This correctly places item and moves top pointer.

3. Final Answer:

   No bug; the code resizes and pushes correctly. -> Option A

4. Quick Check:

   Resize when full, assign then increment top [OK]

Hint: Resize when top equals length; assign then increment top [OK]

Common Mistakes:

• Using wrong resize condition (off by one)
• Incrementing top before assignment
• Assuming top starts at 1 instead of 0

5. You want to implement a dynamic stack that shrinks its internal array size by half when the number of elements falls below one-quarter of the array capacity. Which approach correctly handles this resizing to optimize memory without losing data?

hard

A. Resize array to array.Length * 2 after popping elements to avoid frequent resizing.

B. Resize array to array.Length / 4 whenever an element is popped.

C. After popping, check if top <= array.Length / 4, then resize array to array.Length / 2 using Array.Resize(ref array, newSize).

D. Never shrink the array to avoid complexity; only grow it when full.

Solution

1. Step 1: Understand shrinking condition

   To save memory, shrink when usage is low: top ≤ 1/4 capacity triggers halving the array size.

2. Step 2: Apply resizing correctly

   Use Array.Resize(ref array, array.Length / 2) to shrink safely after popping, preserving existing elements.

3. Final Answer:

   After popping, check if top <= array.Length / 4, then resize array to array.Length / 2 using Array.Resize(ref array, newSize). -> Option C

4. Quick Check:

   Shrink when quarter full using Array.Resize [OK]

Hint: Shrink array when usage ≤ 25% by halving size [OK]

Common Mistakes:

• Shrinking too often causing overhead
• Shrinking to quarter size instead of half
• Not preserving data during resize