DSA Tutorial

Basic Operations of Queue

The following are the basic operations performed on a queue:

• Enqueue: Adds an element to the rear (end) of the queue.
• Dequeue: Removes an element from the front of the queue.
• Peek (Front): Returns the element at the front of the queue without removing it.
• isEmpty: Checks if the queue is empty.
• isFull: Checks if the queue is full (in case of a fixed-size queue).

Types of Queues

There are several types of queues based on how the operations are performed:

• Simple Queue: A basic FIFO queue.
• Circular Queue: A queue where the last position is connected back to the first, allowing better utilization of space.
• Priority Queue: A queue where each element has a priority, and elements are dequeued based on priority.
• Double-Ended Queue (Deque): A queue where elements can be added or removed from both ends.

Queue Implementation

A queue can be implemented using an array or a linked list. Here’s an example of a simple queue implemented using an array:

#include 
#define MAX 5

int queue[MAX];
int front = -1, rear = -1;

void enqueue(int value) {
    if (rear == MAX - 1) {
        printf("Queue is Full\n");
    } else {
        if (front == -1) front = 0;
        rear++;
        queue[rear] = value;
        printf("Enqueued %d\n", value);
    }
}

int dequeue() {
    if (front == -1 || front > rear) {
        printf("Queue is Empty\n");
        return -1;
    } else {
        int dequeued = queue[front];
        front++;
        return dequeued;
    }
}

int peek() {
    if (front == -1 || front > rear) {
        printf("Queue is Empty\n");
        return -1;
    } else {
        return queue[front];
    }
}

int isEmpty() {
    return (front == -1 || front > rear);
}

int main() {
    enqueue(10);
    enqueue(20);
    enqueue(30);
    
    printf("Dequeued: %d\n", dequeue());
    printf("Front: %d\n", peek());
    
    return 0;
}
      

Applications of Queue

Queues are widely used in various applications, including:

• Job Scheduling: Operating systems use queues for job scheduling where jobs are processed in the order they arrive.
• Printer Queues: Print jobs are added to a queue and processed one at a time.
• Call Center Systems: Calls are queued and processed in order of arrival.
• Data Buffering: Queues are used for managing the buffer in streams of data (e.g., video streaming).