This is in C: Declare two structures for this assignment. The first one is a str

Question

This is in C:

Declare two structures for this assignment. The first one is a structure named Node.

This structure will have two members: 1) a pointer to the string to store; and 2) a pointer to the next Node

to build the queue. The second structure is named Queue. This structure will have a single member named

front. This member is a pointer to the the first node in the queue.

Implement a function that constructs a Queue. The constructor allocates the

Queue in the heap, and must return NULL when the constructor is not able to create a Queue. The

Queue must be empty, and to signal this the front pointer must be NULL.

1. Name: CreateQueue

2. Return type: A pointer to the created Queue

Explanation / Answer

Hi Dear,

Please find my implementation:

// A C program to demonstrate linked list based implementation of queue
#include <stdlib.h>
#include <stdio.h>

// A linked list (LL) node to store a queue entry
struct Node
{
    int key;
    struct Node *next;
};

// The queue, front stores the front node of LL and rear stores ths
// last node of LL
struct Queue
{
    struct Node *front, *rear;
};

// A utility function to create a new linked list node.
struct Node* newNode(int k)
{
    struct Node *temp = (struct Node*)malloc(sizeof(struct Node));
    temp->key = k;
    temp->next = NULL;
    return temp;
}

// A utility function to create an empty queue
struct Queue *createQueue()
{
    struct Queue *q = (struct Queue*)malloc(sizeof(struct Queue));
    q->front = q->rear = NULL;
    return q;
}

// The function to add a key k to q
void enQueue(struct Queue *q, int k)
{
    // Create a new LL node
    struct Node *temp = newNode(k);

    // If queue is empty, then new node is front and rear both
    if (q->rear == NULL)
    {
       q->front = q->rear = temp;
       return;
    }

    // Add the new node at the end of queue and change rear
    q->rear->next = temp;
    q->rear = temp;
}

// Function to remove a key from given queue q
struct Node *deQueue(struct Queue *q)
{
    // If queue is empty, return NULL.
    if (q->front == NULL)
       return NULL;

    // Store previous front and move front one node ahead
    struct Node *temp = q->front;
    q->front = q->front->next;

    // If front becomes NULL, then change rear also as NULL
    if (q->front == NULL)
       q->rear = NULL;
    return temp;
}

// Driver Program to test anove functions
int main()
{
    struct Queue *q = createQueue();
    enQueue(q, 10);
    enQueue(q, 20);
    deQueue(q);
    deQueue(q);
    enQueue(q, 30);
    enQueue(q, 40);
    enQueue(q, 50);
    struct Node *n = deQueue(q);
    if (n != NULL)
      printf("Dequeued item is %d", n->key);
    return 0;
}

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