Queue

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A queue is a linear data structure in computer science that follows the First-In-First-Out (FIFO) principle. In a queue, the first element added is the first one to be removed. Think of it as a line of people waiting in a queue, where the person who arrived first is served first.

Key operations and characteristics of a queue:

1. Enqueue (Push): Adding an element to the back (rear) of the queue.

2. Dequeue (Pop): Removing and retrieving the element from the front (front) of the queue.

3. Front (Peek): Retrieving the element from the front of the queue without removing it.

4. Rear: Retrieving the element from the back of the queue without removing it.

5. Empty Check: Checking if the queue is empty.

Common use cases and applications of queues:

1. Breadth-First Search (BFS): Queues are used to implement BFS in graph traversal algorithms. BFS explores neighbors of nodes level by level.

2. Print Queue: Managing print jobs in the order they were received.

3. Task Scheduling: Queues are used in task scheduling systems to manage the execution of tasks in a fair and orderly manner.

4. Bounded Buffers: In producer-consumer scenarios, where data is produced by one process and consumed by another, queues can be used to buffer data.

5. Caching: In web applications, caching systems may use queues to store recently used data and remove the least recently used data.

6. Call Center Systems: Queues can be used to manage incoming calls and assign them to available agents.

Implementing a queue can be done using arrays or linked lists. Here's a simple example of implementing a queue using Python's built-in list:

class Queue:
    def __init__(self):
        self.items = []

    def is_empty(self):
        return len(self.items) == 0

    def enqueue(self, item):
        self.items.append(item)

    def dequeue(self):
        if not self.is_empty():
            return self.items.pop(0)
        else:
            raise Exception("Queue is empty")

    def front(self):
        if not self.is_empty():
            return self.items[0]
        else:
            raise Exception("Queue is empty")

    def rear(self):
        if not self.is_empty():
            return self.items[-1]
        else:
            raise Exception("Queue is empty")

    def size(self):
        return len(self.items)

# Example usage
queue = Queue()

print("Is the queue empty?", queue.is_empty())  # True

queue.enqueue(5)
queue.enqueue(10)
queue.enqueue(7)

print("Front:", queue.front())  # 5
print("Rear:", queue.rear())    # 7
print("Size:", queue.size())     # 3

dequeued_item = queue.dequeue()
print("Dequeued item:", dequeued_item)  # 5
print("Size after dequeue:", queue.size())  # 2

print("Is the queue empty?", queue.is_empty())  # False
 

This example demonstrates a basic queue implementation in Python using a list. However, keep in mind that for more efficient queue operations, especially dequeues in larger queues, using a collections.deque or implementing a queue with a linked list can be more optimal.

 

 

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• Computer Science
• Data Structures