Queue Continued...
Queue
Similar to a stack, the queue also limits the position for inserting and removing am operation on a sequence of data. However, unlike a stack, a queue follows the first in, first out (FIFO) principle.
In Python, a queue can also be implemented using a list. To follow the FIFO principle, the inserting operation occurs at the tail of the list, while the removing operation occurs at the head of the list.Python implementation of a queue
Table of Contents
Queue - An introduction
A Queue is a linear data structure in which data is stored in a First In, First Out manner. In a queue, the item that was added the earliest is removed first. The item that was added more recently is removed last. A queue can be compared to a real-life queue.
enqueue
is a queue operation where you add an item at the back of a queue.
dequeue
is a queue operation where you remove an item from the front of a queue.
Uses of Queues
Operating Systems - often maintain queues while implementing various low-level operations such as CPU Scheduling, Disk Scheduling, etc.
Hardware - hardware interrupts are handled using queues.
Internet - Website traffic handling.
And all other scenarios where a First In, First Out priority has to be implemented.
Implementing Queues
Queue Methods
queue.Enqueue()
The
queue.Enqueue()
method adds an element at the rear of the queue.Time Complexity -> O(1)
queue.Dequeue()
The
queue.Dequeue()
method removes an element from the front of the queue.Time Complexity -> O(1)
queue.Front()
The
queue.Front()
method returns the front item from the queue.Time Complexity -> O(1)
queue.Rear()
The
queue.Rear()
method returns the rear item from the queue.Time Complexity -> O(1)
queue.isEmpty()
The
queue.isEmpty()
method returnsTrue
if the queue is empty, else returnsFalse
.Time Complexity -> O(1)
Queues can be implemented in various ways. Let us look at how to implement a queue using a list and using the collections.deque
module in Python.
Queue using a List
We can use the list methods insert
and pop
to implement a queue.
Queue using collections.Deque
The deque
class from the python collections
module can also be used to implement a queue. This method of implementing a queue is far more efficient because deque provides faster enqueue and dequeue operations.
Practice Queues
Try implementing the queue in Python first. Then once you’re done with the implementation, try solving these problems on HackerRank and LeetCode
Reversing a Queue - GeeksforGeeks
Sort the Queue using Recursion - GeeksforGeeks
Reversing First K Elements of the Queue - GeeksforGeeks
Implementing Stack using Queues - GeeksforGeeks
Queries with Fixed Length - HackerRank
Truck Tour - HackerRank
Maximum Sum of Triangle No Less Than K - LeetCode
Design Circular Queue - LeetCode
Design Circular Dequeue - LeetCode
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