Dequeue Operation in DSA Typescript - Build from Scratch

Dequeue Operation

📖 Scenario: Imagine you are managing a line of customers waiting for service. Sometimes, customers leave from the front or the back of the line. You want to keep track of the line and remove customers from either end as needed.

🎯 Goal: You will create a double-ended queue (deque) using an array, then remove customers from the front and back, and finally display the remaining customers in the line.

📋 What You'll Learn

Create an array called deque with exact string elements representing customers in order

Create two variables called frontRemove and backRemove to store the removed customers

Remove one customer from the front of the deque and store it in frontRemove

Remove one customer from the back of the deque and store it in backRemove

Print the removed customers and the remaining deque in order

💡 Why This Matters

🌍 Real World

Managing lines or queues where people or items can enter or leave from both ends, like customer service lines or task scheduling.

💼 Career

Understanding deque operations is useful for software development roles involving data structure manipulation, real-time systems, and performance optimization.

1

Create the initial deque

Create an array called deque with these exact string elements in order: 'Alice', 'Bob', 'Charlie', 'Diana', 'Ethan'

DSA Typescript

# Your code here

Hint

Use const deque: string[] = [...] to create the array with the exact names.

2

Create variables to store removed customers

Create two variables called frontRemove and backRemove and initialize them with empty strings ''

DSA Typescript

const deque: string[] = ['Alice', 'Bob', 'Charlie', 'Diana', 'Ethan'];
# Your code here

Hint

Use let frontRemove: string = ''; and let backRemove: string = ''; to create the variables.

3

Remove customers from front and back

Remove one customer from the front of deque using shift() and assign it to frontRemove. Remove one customer from the back of deque using pop() and assign it to backRemove.

DSA Typescript

const deque: string[] = ['Alice', 'Bob', 'Charlie', 'Diana', 'Ethan'];
let frontRemove: string = '';
let backRemove: string = '';
# Your code here

Hint

Use deque.shift() to remove from front and deque.pop() to remove from back.

4

Print removed customers and remaining deque

Print the removed customers using console.log in this exact format: Removed from front: Alice and Removed from back: Ethan. Then print the remaining deque in order using console.log with this exact format: Remaining deque: Bob, Charlie, Diana

DSA Typescript

const deque: string[] = ['Alice', 'Bob', 'Charlie', 'Diana', 'Ethan'];
let frontRemove: string = '';
let backRemove: string = '';
frontRemove = deque.shift()!;
backRemove = deque.pop()!;
# Your code here

Hint

Use console.log with template strings and deque.join(', ') to print the results.

Practice

1. What is the main difference between a dequeue and a queue?

easy

A. A dequeue allows insertion and deletion from both ends.

B. A dequeue only allows insertion at the rear.

C. A dequeue only allows deletion from the front.

D. A dequeue is a fixed size data structure.

Solution

1. Step 1: Understand queue operations

   A queue allows insertion at the rear and deletion from the front only.

2. Step 2: Understand dequeue operations

   A dequeue allows insertion and deletion at both front and rear ends.

3. Final Answer:

   A dequeue allows insertion and deletion from both ends. -> Option A

4. Quick Check:

   Dequeue = Both ends operations [OK]

Hint: Dequeue = Double-ended queue, both ends allowed [OK]

Common Mistakes:

• Thinking dequeue is same as queue
• Assuming insertion only at rear
• Confusing dequeue with stack

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

easy

A. dequeue.pushFront(element);

B. dequeue.unshift(element);

C. dequeue.addFirst(element);

D. dequeue.insertFront(element);

Solution

1. Step 1: Recall array methods for front insertion

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

2. Step 2: Check other options

   Methods like pushFront, addFirst, insertFront do not exist in standard arrays.

3. Final Answer:

   dequeue.unshift(element); -> Option B

4. Quick Check:

   Array front insert = unshift() [OK]

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

Common Mistakes:

• Using push() instead of unshift()
• Assuming pushFront() exists
• Confusing with linked list methods

3. Consider this TypeScript code using an array as a dequeue:

let dequeue = [10, 20, 30];
dequeue.pop();
dequeue.unshift(5);
console.log(dequeue);

What is the output?

medium

A. [5, 10, 20]

B. [5, 10, 20, 30]

C. [10, 20, 30, 5]

D. [10, 20]

Solution

1. Step 1: Execute pop()

   pop() removes last element 30, so array becomes [10, 20].

2. Step 2: Execute unshift(5)

   unshift(5) adds 5 at front, array becomes [5, 10, 20].

3. Final Answer:

   [5, 10, 20] -> Option A

4. Quick Check:

   pop removes last, unshift adds front [OK]

Hint: pop removes last, unshift adds front [OK]

Common Mistakes:

• Assuming pop removes front
• Thinking unshift adds at end
• Confusing array order after operations

4. The following TypeScript code tries to remove an element from the front of a dequeue implemented as an array:

let dequeue = [1, 2, 3];
dequeue.removeFront();
console.log(dequeue);

What is the issue and how to fix it?

medium

A. removeFront() works only on linked lists; convert array to linked list.

B. removeFront() removes last element; use pop() instead.

C. removeFront() is not a valid method; use shift() instead.

D. No issue; code runs correctly.

Solution

1. Step 1: Identify invalid method

   Arrays in TypeScript do not have removeFront() method; this causes a runtime error.

2. Step 2: Use correct method for front removal

   shift() removes the first element from an array correctly.

3. Final Answer:

   removeFront() is not a valid method; use shift() instead. -> Option C

4. Quick Check:

   Front removal in arrays = shift() [OK]

Hint: Use shift() to remove front element in arrays [OK]

Common Mistakes:

• Using non-existent removeFront() method
• Confusing pop() with front removal
• Thinking arrays have linked list methods

5. You have a dequeue implemented as an array: let dq = [1, 2, 3, 4];. You perform these operations:

dq.pop();
dq.unshift(0);
dq.push(5);
dq.shift();
console.log(dq);

What is the final state of the dequeue?

hard

A. [0, 1, 2, 3, 5]

B. [2, 3, 4, 5]

C. [1, 2, 3, 4, 5]

D. [1, 2, 3, 5]

Solution

1. Step 1: Execute pop()

   pop() removes last element 4, dq becomes [1, 2, 3].

2. Step 2: Execute unshift(0)

   unshift(0) adds 0 at front, dq becomes [0, 1, 2, 3].

3. Step 3: Execute push(5)

   push(5) adds 5 at end, dq becomes [0, 1, 2, 3, 5].

4. Step 4: Execute shift()

   shift() removes first element 0, dq becomes [1, 2, 3, 5].

5. Final Answer:

   [1, 2, 3, 5] -> Option D

6. Quick Check:

   pop removes end, unshift adds front, push adds end, shift removes front [OK]

Hint: Track each operation stepwise on array [OK]

Common Mistakes:

• Forgetting shift removes front element
• Mixing order of operations
• Assuming unshift adds at end