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

Practice - 5 Tasks

1fill in blank

easy

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

DSA Javascript

function push(stack, element) {
  stack.[1](element);
}

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

Apush

Binsert

Cappend

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using append which is not a JavaScript array method.

Using insert which is not a standard array method in JavaScript.

In JavaScript, the push() method adds an element to the end of an array, which is how we add to the top of an array-based stack.

2fill in blank

medium

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

DSA Javascript

function pop(stack) {
  if (!stack.head) return null;
  const value = stack.head.value;
  stack.head = stack.head.[1];
  return value;
}

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

Alink

Bnext

Cchild

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is used in doubly linked lists but not singly linked lists.

Using 'link' or 'child' which are not standard property names.

In a linked list, each node points to the next node using the 'next' property. To pop, we move the head to the next node.

3fill in blank

hard

Fix the error in the code that checks if an array stack is empty.

DSA Javascript

function isEmpty(stack) {
  return stack.[1] === 0;
}

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

Alength

Bsize

Ccount

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' which is used in some other languages or data structures.

Using 'count' or 'total' which are not JavaScript array properties.

JavaScript arrays use the 'length' property to indicate how many elements they contain.

4fill in blank

hard

Fill both blanks to create a linked list node and link it as the new head of the stack.

DSA Javascript

function push(stack, value) {
  const newNode = { value: value, [1]: stack.[2] };
  stack.head = newNode;
}

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

Anext

Bprev

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for backward links in doubly linked lists.

Using 'tail' which points to the end, not the top of the stack.

The new node's 'next' points to the current head, then the head is updated to the new node.

5fill in blank

hard

Fill all three blanks to create a function that returns the top element of an array stack without removing it.

DSA Javascript

function peek(stack) {
  if (stack.[1] === 0) return null;
  return stack[stack.[2] [3] 1];
}

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

Alength

Bsize

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' which is not a JavaScript array property.

Using '+' instead of '-' which would cause an index out of range.

We check if the array length is zero, then return the last element at index length - 1.

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 overall

D. Simpler syntax to implement

Solution

1. Step 1: Understand stack size behavior in arrays

   Arrays have fixed size or need resizing which costs time and memory.

2. Step 2: Understand linked list size behavior

   Linked lists grow dynamically by adding nodes without resizing.

3. Final Answer:

   Dynamic size without needing to resize -> Option A

4. Quick Check:

   Linked list stacks grow dynamically = B [OK]

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

Common Mistakes:

• Thinking arrays resize automatically without cost
• Confusing access speed advantage
• Assuming linked lists use less memory

2. Which of the following is the correct way to push an element onto a stack implemented using an array in JavaScript?

easy

A. stack.insert(element);

B. stack.add(element);

C. stack.append(element);

D. stack.push(element);

Solution

1. Step 1: Recall JavaScript array methods

   The method to add an element at the end of an array is push().

2. Step 2: Match method to stack push operation

   Stack push adds element on top, which is end of array, so push() is correct.

3. Final Answer:

   stack.push(element); -> Option D

4. Quick Check:

   Array push method = stack.push(element) [OK]

Hint: Use push() to add element at array end [OK]

Common Mistakes:

• Using non-existent methods like add() or append()
• Confusing push with pop
• Trying to use insert() which is not an array method

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

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

class Stack {
  constructor() {
    this.top = null;
  }
  push(value) {
    const node = new Node(value);
    node.next = this.top;
    this.top = node;
  }
  pop() {
    if (!this.top) return null;
    const val = this.top.value;
    this.top = this.top.next;
    return val;
  }
}

const stack = new Stack();
stack.push(10);
stack.push(20);
console.log(stack.pop());
console.log(stack.pop());
console.log(stack.pop());

What is the output?

medium

A. 20
10
null

B. 10
20
null

C. null
10
20

D. 20
null
10

Solution

1. Step 1: Trace push operations

   Push 10: top points to node with value 10. Push 20: top points to node with value 20, next points to 10.

2. Step 2: Trace pop operations

   First pop returns 20, top moves to node with 10. Second pop returns 10, top becomes null. Third pop returns null as stack is empty.

3. Final Answer:

   20 10 null -> Option A

4. Quick Check:

   Stack LIFO pop order = 20, 10, null [OK]

Hint: Stack pops last pushed first (LIFO) [OK]

Common Mistakes:

• Assuming FIFO order instead of LIFO
• Forgetting to return null when empty
• Mixing push and pop order

4. The following code attempts to implement a stack using an array but has a bug:

class Stack {
  constructor() {
    this.items = [];
  }
  push(element) {
    this.items[this.items.length] = element;
  }
  pop() {
    return this.items.pop;
  }
}

What is the error and how to fix it?

medium

A. push method should use push() instead of indexing

B. pop method is missing parentheses; fix by using this.items.pop()

C. items array should be initialized as null

D. pop method should return this.items.pop without parentheses

Solution

1. Step 1: Identify pop method usage

   pop is a function, so calling this.items.pop without () returns the function itself, not the popped element.

2. Step 2: Fix pop method call

   Add parentheses to call the function: this.items.pop() returns the last element and removes it.

3. Final Answer:

   pop method is missing parentheses; fix by using this.items.pop() -> Option B

4. Quick Check:

   Call pop() with parentheses to execute [OK]

Hint: Remember to call pop() as a function with () [OK]

Common Mistakes:

• Forgetting parentheses on pop() call
• Changing push to incorrect method
• Initializing items as null instead of array

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

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

hard

A. Array stack, because it has faster push and pop operations always

B. Array stack, because arrays use less memory per element

C. Linked list stack, because it grows dynamically and avoids resizing overhead

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

Solution

1. Step 1: Consider resizing overhead in array stacks

   Arrays need resizing when full, which is costly for millions of operations.

2. Step 2: Consider linked list memory and dynamic growth

   Linked lists grow node by node, avoiding resizing and memory waste from unused array slots.

3. Final Answer:

   Linked list stack, because it grows dynamically and avoids resizing overhead -> Option C

4. Quick Check:

   Dynamic growth avoids resizing overhead = A [OK]

Hint: For huge stacks, linked lists avoid costly resizing [OK]

Common Mistakes:

• Assuming arrays always have faster push/pop
• Ignoring resizing cost in arrays
• Thinking linked lists allow random access