Queues

Tarun Luthra

Agenda

What you will learn?

• Basics of Queues

• Implementation

• Examples

Queues

The Queue in data structure is an ordered, linear sequence of items. It is a FIFO (First In First Out) data structure, which means that we can insert an item to the rear end of the queue and remove from the front of the queue only. A Queue is a sequential data type, unlike an array, in an array, we can access any of its elements using indexing, but we can only access the element at the front of the queue at a time.

1. push(x)

1. push(x)

: insert x at the rear

1. push(x)
2. pop()

: insert x at the rear

1. push(x)
2. pop()

: insert x at the rear

: delete the front element

1. push(x)
2. pop()
3. front()

: insert x at the rear

: delete the front element

1. push(x)
2. pop()
3. front()

: insert x at the rear

: delete the front element

: return the front element

1. push(x)
2. pop()
3. front()
4. rear()

: insert x at the rear

: delete the front element

: return the front element

1. push(x)
2. pop()
3. front()
4. rear()

: insert x at the rear

: delete the front element

: return the front element

: return the rear/back element

1. push(x)
2. pop()
3. front()
4. rear()
5. size()

: insert x at the rear

: delete the front element

: return the front element

: return the rear/back element

1. push(x)
2. pop()
3. front()
4. rear()
5. size()

: insert x at the rear

: delete the front element

: return the front element

: return the rear/back element

: return no of elements

1. enqueue(x) / push(x)
2. dequeue() / pop()
3. front()
4. rear()
5. size()

: insert x at the rear

: delete the front element

: return the front element

: return the rear/back element

: return no of elements

Can we iterate over a queue ? 🧐

Not without removing the data.

Can we iterate over a queue ? 🧐

Queue Libraries

There are ready-made implementations of Queue in most language's libraries/modules. You can find them here :

1. Queues in C -
   https://www.scaler.com/topics/c/implementation-of-queue-using-linked-list/

2. Queues in Java -
   https://www.scaler.com/topics/java/stack-and-queue-in-java/

3. Queues in Python -
   https://www.scaler.com/topics/queue-in-python/

Visualisers

1. Queue Visualiser - Array Implementation -https://www.cs.usfca.edu/~galles/visualization/QueueArray.html
2. Queue Visualiser - Linked List Implementation -
   https://visualgo.net/en/list?slide=1-1

Codes

1. Java LL Implementation :
   https://ide.codingminutes.com/?id=aat
2. Python LL Implementation :
   https://ide.codingminutes.com/?id=aac

Thank you! 👨‍💻