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Queue | Unit-2 | DSA

 https://www.programiz.com/dsa/queue


Array Implementaion of queue:

#include <stdio.h>


#define MAX_SIZE 100 // Maximum size of the queue


int queue[MAX_SIZE]; // Array to store the queue elements

int front = -1;      // Front of the queue

int rear = -1;       // Rear of the queue


// Function to check if the queue is empty

int is_empty() {

    return (front == -1 && rear == -1);

}


// Function to check if the queue is full

int is_full() {

    return (rear == MAX_SIZE - 1);

}


// Function to insert an element into the queue

void enqueue(int value) {

    if (is_full()) {

        printf("Queue Overflow\n");

        return;

    }

    if (is_empty()) {

        front = rear = 0; // If the queue is empty, initialize front and rear to 0

    } else {

        rear++; // Move rear to the next position

    }

    queue[rear] = value; // Insert the value at the rear position

}


// Function to remove an element from the queue

int dequeue() {

    if (is_empty()) {

        printf("Queue Underflow\n");

        return -1;

    }

    int dequeued_element = queue[front]; // Get the element at the front

    if (front == rear) {

        front = rear = -1; // If the queue has only one element, reset front and rear

    } else {

        front++; // Move front to the next position

    }

    return dequeued_element; // Return the removed element

}


// Function to display the queue elements

void display() {

    if (is_empty()) {

        printf("Queue is empty\n");

        return;

    }

    printf("Queue elements are: ");

    for (int i = front; i <= rear; i++) {

        printf("%d ", queue[i]);

    }

    printf("\n");

}


int main() {

    // Insert elements into the queue

    enqueue(10);

    enqueue(20);

    enqueue(30);


    // Display the queue

    display();


    // Remove an element from the queue

    printf("Dequeued element: %d\n", dequeue());


    // Display the updated queue

    display();


    return 0;

}


Linked list  Implementaion of Queue:


#include <stdio.h>
#include <stdlib.h>

// Node structure for the linked list
struct Node {
    int data;
    struct Node* next;
};

// Structure for the queue
struct Queue {
    struct Node *front, *rear;
};

// Function to create a new node
struct Node* createNode(int value) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    if (!newNode) {
        printf("Memory allocation failed.\n");
        exit(1);
    }
    newNode->data = value;
    newNode->next = NULL;
    return newNode;
}

// Function to initialize an empty queue
struct Queue* createQueue() {
    struct Queue* queue = (struct Queue*)malloc(sizeof(struct Queue));
    if (!queue) {
        printf("Memory allocation failed.\n");
        exit(1);
    }
    queue->front = queue->rear = NULL;
    return queue;
}

// Function to check if the queue is empty
int is_empty(struct Queue* queue) {
    return (queue->front == NULL);
}

// Function to enqueue an element into the queue
void enqueue(struct Queue* queue, int value) {
    struct Node* newNode = createNode(value);
    if (is_empty(queue)) {
        queue->front = queue->rear = newNode;
    } else {
        queue->rear->next = newNode;
        queue->rear = newNode;
    }
}

// Function to dequeue an element from the queue
int dequeue(struct Queue* queue) {
    if (is_empty(queue)) {
        printf("Queue underflow\n");
        exit(1);
    }
    int value = queue->front->data;
    struct Node* temp = queue->front;
    queue->front = queue->front->next;
    free(temp);
    return value;
}

// Function to display the queue elements
void display(struct Queue* queue) {
    if (is_empty(queue)) {
        printf("Queue is empty\n");
        return;
    }
    struct Node* current = queue->front;
    printf("Queue elements are: ");
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

int main() {
    struct Queue* queue = createQueue();

    // Enqueue elements into the queue
    enqueue(queue, 10);
    enqueue(queue, 20);
    enqueue(queue, 30);

    // Display the queue
    display(queue);

    // Dequeue an element from the queue
    printf("Dequeued element: %d\n", dequeue(queue));

    // Display the updated queue
    display(queue);

    return 0;
}


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