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

Practice - 5 Tasks

1fill in blank

easy

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

DSA Typescript

stack.[1](value);

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

Apush

Bpop

Cshift

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push

Using shift or unshift which affect the start of the array

To add an element to the top of an array stack, we use the push method.

2fill in blank

medium

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

DSA Typescript

const newNode = { value: val, [1]: null };

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

Aprev

Bhead

Cnext

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists

Using 'head' or 'tail' which are list references, not node pointers

Each node in a linked list stack points to the next node using the next property.

3fill in blank

hard

Fix the error in popping an element from an array stack.

DSA Typescript

const popped = stack.[1]();

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

Aunshift

Bpush

Cshift

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using push which adds instead of removes

Using shift or unshift which remove or add at the start

To remove the top element from an array stack, use the pop method.

4fill in blank

hard

Fill both blanks to correctly push a node onto a linked list stack.

DSA Typescript

newNode.[1] = this.[2];
this.head = newNode;

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

Anext

Bprev

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next'

Using 'tail' instead of 'head'

When pushing a node, set its next to the current head, then update head to the new node.

5fill in blank

hard

Fill all three blanks to check if the array stack is empty.

DSA Typescript

if (stack.[1] === [2]) {
  return [3];
}

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

Alength

B0

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for length > 0

Returning false when empty

To check if the stack is empty, compare length to 0 and return true if empty.

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. Dynamic size without needing to resize

B. Faster access to elements by index

C. Uses less memory per element

D. Simpler syntax to implement

Solution

1. Step 1: Understand stack size behavior

   Arrays have fixed size or require resizing, linked lists grow dynamically.

2. Step 2: Compare memory and access

   Linked lists use extra memory for pointers and have slower indexed access.

3. Final Answer:

   Dynamic size without needing to resize -> Option A

4. Quick Check:

   Linked list stacks grow dynamically = A [OK]

Hint: Linked list stacks grow dynamically, arrays need resizing [OK]

Common Mistakes:

• Thinking arrays always use less memory
• Confusing access speed advantages
• Assuming linked lists have simpler syntax

2. Which TypeScript syntax correctly declares an array-based stack of numbers?

easy

A. let stack = new Stack<number>();

B. const stack: number[] = [];

C. const stack: Array = number[];

D. var stack: number = [];

Solution

1. Step 1: Check array declaration syntax

   TypeScript arrays use type[] or Array<type> syntax.

2. Step 2: Validate each option

   const stack: number[] = []; uses correct syntax: number[] = []. Others have syntax errors or wrong types.

3. Final Answer:

   const stack: number[] = []; -> Option B

4. Quick Check:

   Correct array syntax = C [OK]

Hint: Array type syntax is type[] or Array<type> [OK]

Common Mistakes:

• Using wrong generic syntax
• Assigning array to wrong type variable
• Using var instead of const/let incorrectly

3. Consider this TypeScript code using an array stack:

const stack: number[] = [];
stack.push(10);
stack.push(20);
stack.pop();
stack.push(30);
console.log(stack);

What is the output?

medium

A. [10, 30]

B. [30]

C. [20, 30]

D. [10, 20, 30]

Solution

1. Step 1: Trace stack operations

   Push 10 -> [10], push 20 -> [10,20], pop removes 20 -> [10], push 30 -> [10,30]

2. Step 2: Check final stack content

   Stack contains 10 and 30 in order pushed and popped.

3. Final Answer:

   [10, 30] -> Option A

4. Quick Check:

   Push/pop trace = [10, 30] [OK]

Hint: Pop removes last pushed element, check stack after each step [OK]

Common Mistakes:

• Forgetting pop removes last element
• Assuming pop removes first element
• Confusing push order

4. This TypeScript code tries to implement a linked list stack but has an error:

class Node {
  value: number;
  next: Node | null;
  constructor(value: number) {
    this.value = value;
    this.next = null;
  }
}

class Stack {
  top: Node | null = null;
  push(value: number) {
    const newNode = new Node(value);
    newNode.next = this.top;
    this.top = newNode;
  }
  pop(): number | null {
    if (!this.top) return null;
    const val = this.top.value;
    this.top = this.top.next;
    return val;
  }
}

const stack = new Stack();
stack.push(5);
stack.push(10);
console.log(stack.pop());
console.log(stack.pop());
console.log(stack.pop());

What is the error in this code?

medium

A. Node class is missing a constructor

B. push() does not update the top pointer correctly

C. pop() returns null when stack is empty, which is correct behavior

D. Stack class does not initialize top to null

Solution

1. Step 1: Review pop() method behavior

   pop() returns null if stack is empty, which is expected to indicate empty stack.

2. Step 2: Check push() and initialization

   push() correctly updates top; Node has constructor; top initialized to null.

3. Final Answer:

   pop() returns null when stack is empty, which is correct behavior -> Option C

4. Quick Check:

   pop() returns null on empty stack = A [OK]

Hint: pop() returning null on empty stack is expected [OK]

Common Mistakes:

• Thinking pop() should throw error instead
• Believing push() does not update top
• Missing that top is initialized properly

5. You want to implement a stack that can handle millions of push/pop operations efficiently without resizing overhead. Which implementation is better and why?

hard

A. Array stack, because arrays have faster indexed access

B. Linked list stack, because it uses contiguous memory

C. Array stack, because it uses less memory per element

D. Linked list stack, because it avoids costly array resizing

Solution

1. Step 1: Consider resizing overhead in array stacks

   Arrays must resize and copy data when full, causing delays in many operations.

2. Step 2: Evaluate linked list advantages

   Linked lists grow dynamically without resizing, so push/pop remain efficient for large operations.

3. Final Answer:

   Linked list stack, because it avoids costly array resizing -> Option D

4. Quick Check:

   Dynamic growth avoids resizing = B [OK]

Hint: Avoid resizing overhead with linked list stacks for large operations [OK]

Common Mistakes:

• Assuming arrays never resize
• Confusing memory usage with speed
• Thinking linked lists use contiguous memory