queue_by_LL.c

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

struct Node {
    int data;
    struct Node* next;
};

struct Queue {
    struct Node *front, *rear;
};

struct Node* newNode(int data) {
    struct Node* temp = (struct Node*)malloc(sizeof(struct Node));
    temp->data = data;
    temp->next = NULL;
    return temp;
}

struct Queue* createQueue() {
    struct Queue* q = (struct Queue*)malloc(sizeof(struct Queue));
    q->front = q->rear = NULL;
    return q;
}

void enqueue(struct Queue* q, int data) {
    struct Node* temp = newNode(data);


    if (q->rear == NULL) {
        q->front = q->rear = temp;
        return;
    }


    q->rear->next = temp;
    q->rear = temp;
}

int dequeue(struct Queue* q) {

    if (q->front == NULL) {
        printf("Queue is empty\n");
        return -1;
    }

    struct Node* temp = q->front;
    q->front = q->front->next;

    if (q->front == NULL)
        q->rear = NULL;

    int data = temp->data;
    free(temp);
    return data;
}

void displayQueue(struct Queue* q) {
    struct Node* temp = q->front;
    while (temp != NULL) {
        printf("%d -> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}


int main() {
    struct Queue* q = createQueue();
    
    enqueue(q, 10);
    enqueue(q, 20);
    enqueue(q, 30);
    
    printf("Queue: ");
    displayQueue(q);

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

    printf("Queue after dequeue: ");
    displayQueue(q);

    return 0;
}