Double Ended Queue Deque in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element at the front of the deque.

DSA Typescript

deque.[1](10);

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

ApushBack

Benqueue

CpushFront

DpopFront

Attempts:

3 left

💡 Hint

Common Mistakes

Using pushBack adds to the end, not the front.

enqueue is usually for queues, not deques.

popFront removes, it does not add.

To add an element at the front of a deque, use pushFront.

2fill in blank

medium

Complete the code to remove an element from the back of the deque.

DSA Typescript

const removed = deque.[1]();

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

ApopBack

BpopFront

Cdequeue

DremoveBack

Attempts:

3 left

💡 Hint

Common Mistakes

popFront removes from the front, not the back.

dequeue is usually for queues, removing from front.

removeBack is not a standard method name.

To remove an element from the back of a deque, use popBack.

3fill in blank

hard

Fix the error in the code to check if the deque is empty.

DSA Typescript

if (deque.[1]()) {
  console.log('Deque is empty');
}

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

AisEmpty

BisFull

Cempty

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using isFull checks if deque is full, not empty.

empty is not a method but could be a property.

size returns number, not boolean.

The method isEmpty() checks if the deque has no elements.

4fill in blank

hard

Fill both blanks to create a deque from an array and add an element at the back.

DSA Typescript

const deque = new Deque([1]);
deque.[2](20);

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

A[1, 2, 3]

BpushBack

CpushFront

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using pushFront adds at the front, not back.

Initializing with empty array won't show initial elements.

Passing a non-array value causes errors.

Initialize deque with an array [1, 2, 3] and add 20 at the back using pushBack.

5fill in blank

hard

Fill all three blanks to remove from front, add at front, and check size.

DSA Typescript

deque.[1]();
deque.[2](5);
const size = deque.[3];

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

ApopFront

BpushFront

Clength

DpopBack

Attempts:

3 left

💡 Hint

Common Mistakes

Using popBack removes from back, not front.

Using pushBack adds at back, not front.

Trying to call size as a method instead of property.

Remove from front with popFront(), add 5 at front with pushFront(5), and get size with length.

Practice

1. What is a Double Ended Queue (Deque)?

easy

A. A data structure where elements can be added or removed from both ends

B. A queue where elements can only be added at the rear and removed from the front

C. A stack where elements can only be added or removed from the top

D. A list that allows random access to elements

Solution

1. Step 1: Understand the definition of a deque

   A deque allows insertion and deletion from both front and rear ends, unlike a queue or stack.

2. Step 2: Compare with other data structures

   Queue allows operations only at one end for insertion and the other for deletion; stack only at one end.

3. Final Answer:

   A data structure where elements can be added or removed from both ends -> Option A

4. Quick Check:

   Deque = double-ended queue [OK]

Hint: Deque means double-ended queue, both ends usable [OK]

Common Mistakes:

• Confusing deque with stack or queue
• Thinking deque allows random access
• Assuming insertion only at one end

2. Which of the following is the correct TypeScript method to add an element at the front of a deque implemented as an array named deque?

easy

A. deque.shift(element);

B. deque.push(element);

C. deque.pop(element);

D. deque.unshift(element);

Solution

1. Step 1: Recall array methods for front insertion

   In TypeScript/JavaScript, unshift() adds an element at the start of an array.

2. Step 2: Verify other methods

   push() adds at the end, pop() removes from end, shift() removes from front.

3. Final Answer:

   deque.unshift(element); -> Option D

4. Quick Check:

   unshift() adds front [OK]

Hint: Use unshift() to add front in arrays [OK]

Common Mistakes:

• Using push() instead of unshift() for front
• Confusing pop() and shift() as insertion
• Passing arguments to pop() or shift()

3. What will be the output of the following TypeScript code?

const deque: number[] = [];
deque.push(10);
deque.unshift(20);
deque.push(30);
deque.shift();
console.log(deque);

medium

A. [20, 10, 30]

B. [20, 30]

C. [10, 30]

D. [30, 20]

Solution

1. Step 1: Trace each operation on deque

   Start: []
   push(10) -> [10]
   unshift(20) -> [20, 10]
   push(30) -> [20, 10, 30]
   shift() removes front -> removes 20 -> [10, 30]

2. Step 2: Final state of deque

   After all operations, deque is [10, 30].

3. Final Answer:

   [10, 30] -> Option C

4. Quick Check:

   After shift(), front removed -> [10, 30] [OK]

Hint: Remember shift() removes front element [OK]

Common Mistakes:

• Forgetting shift() removes front
• Mixing order of push and unshift
• Assuming shift() removes last element

4. Identify the error in the following TypeScript code that implements a deque using an array:

const deque: number[] = [];
deque.push(5);
deque.unshift(10);
deque.pop(5);
console.log(deque);

medium

A. push() cannot be used on arrays

B. pop() should not have any arguments

C. unshift() removes elements, not adds

D. console.log syntax is incorrect

Solution

1. Step 1: Check usage of pop() method

   pop() removes the last element and does not take any arguments. Passing 5 is incorrect.

2. Step 2: Verify other methods and syntax

   push() adds element at end, unshift() adds at front, console.log syntax is correct.

3. Final Answer:

   pop() should not have any arguments -> Option B

4. Quick Check:

   pop() takes no arguments [OK]

Hint: pop() never takes arguments [OK]

Common Mistakes:

• Passing argument to pop()
• Confusing unshift() as removal
• Thinking push() is invalid on arrays

5. You want to implement a deque that supports adding and removing elements from both ends efficiently. Which data structure is best suited for this in TypeScript, and why?

hard

A. Use a linked list because it allows O(1) insertion and deletion at both ends

B. Use an array because it provides O(1) insertion and deletion at both ends

C. Use a binary tree because it supports fast search and insertion

D. Use a stack because it supports adding/removing from both ends

Solution

1. Step 1: Analyze efficiency of array for deque operations

   Arrays have O(1) insertion/deletion at the end but O(n) at the front due to shifting elements.

2. Step 2: Consider linked list advantages

   Linked lists allow O(1) insertion and deletion at both front and rear by adjusting pointers.

3. Step 3: Evaluate other options

   Binary trees are for search, not efficient deque operations; stacks only allow one end operations.

4. Final Answer:

   Use a linked list because it allows O(1) insertion and deletion at both ends -> Option A

5. Quick Check:

   Linked list = efficient deque [OK]

Hint: Linked list supports fast front and rear operations [OK]

Common Mistakes:

• Assuming arrays are efficient at front insertion
• Confusing stack with deque
• Choosing binary tree for deque operations