Question

Suppose we want to implement a circular queue using an array that has an initial capacity (maximum number of elements) MAX. A circular queue is like a regular queue except that elements can be enqueued or dequeued by wrapping around it. Assume we enqueue on the tail and dequeue from the head. An example circular queue with sample operations is shown below: head head tail head tail tail head Enqueue(9) a) Write a program in C that implements this circular queue while keeping track of its head and tail indices and number of elements in the queue. If we enqueue while the queue is full, create a new queue double the size, insert all elements from the old queue into the new one, and enqueue the new element (see example above). If we dequeue while the queue is empty, print “Queue underflow". You may assume the following: • • The queue structure contains five members: array of nonzero integers, capacity, size, head, and tail An "empty" element is represented by a 0. Your program should contain functions to initialize a queue to MAX size, enqueue a nonzero integer, dequeue an integer from a queue and return it, and deallocate all memory taken up by the queue. You never need to shrink the capacity of the queue. • b) Suppose we implemented the circular queue using a linked list instead of an array. How would this affect the time and space complexity of the enqueue and dequeue operations?

Answer 1

I HAVE IMPLEMENTED THE CIRCULAR QUEUE WITH THE REQUIRED OPERATIONS DESCRIBED ABOVE.

I HAVE ALSO INCLUDED THE COMMENTS TO DESCRIBE THE OPERATIONS.

ANY FURTHER CLARIFICATION REQUIRED LEAVE A COMMENT:

//program to implement circular queue #include<stdio.h> #include<stdlib.h> #define MAX 3 struct queue {    int *ele;    int capacity,size;    int head,tail; }; typedef struct queue QUEUE; /*INITILIZATION OF QUEUE STRUCTURE*/ void initialize(QUEUE *q) { q->capacity=MAX; q->ele=(int*)calloc(q->capacity,sizeof(int)); q->head=0; q->tail=0; q->size=0; } /*TO ADD AN ELEMENT TO QUEUE*/ void enqueue(QUEUE *q) { int ele; if(q->size<q->capacity) { printf("\n\t....ENTER AN ELEMENT \t"); scanf("%d",&ele); q->ele[q->tail]=ele; q->tail=(q->tail+1)%q->capacity; q->size++; printf("\n\t....ELEMENT ENQUEUED SUCCESSFULLY \n"); }else { /*IF THE QUEUE IS FULL DOUBLE ITS SIZE */    q->tail=q->capacity;    q->capacity=q->capacity*2;    q->ele=(int*)realloc(q->ele,q->capacity*sizeof(int));    printf("\n\t....ENTER AN ELEMENT \t"); scanf("%d",&ele); q->ele[q->tail]=ele; q->tail=(q->tail+1)%q->capacity; q->size++; printf("\n\t....ELEMENT ENQUEUED SUCCESSFULLY \n"); } } /*TO REMOVE AN ELEMENT TO QUEUE*/ void dequeue(QUEUE *q) { if(q->size==0) {    printf("\n\t....QUEUE UNDERFLOW\n\t");    initialize(q); } else {    printf("\n\t....THE REMOVED ELEMENT IS %d\n\t",q->ele[q->head]); q->ele[q->head]=0; q->head=(q->head+1)%q->capacity; q->size--; } } /*TO PRINT ELEMENTS FROM QUEUE*/ void print(QUEUE *q) {    int i=q->head;    int cnt=q->size;    printf("\n\t....ELEMENTS IN THE QUEUE ARE\n\t");    while(cnt!=0)    {        printf("\t %d",q->ele[i]);        i=(i+1)%q->capacity;        cnt--;    } } void main() {    int choice;    QUEUE q;    initialize(&q);    printf("\n\t....CIRCULAR QUEUE PROGRAM USING ARRAYS....\n");    while(1)    { printf("\n\t....1.ENQUEUE\t2.DEQUEUE\t3.PRINT\t4.EXIT\n\t....Enter your choice :");        scanf("%d",&choice);        switch(choice)        {        case 1:enqueue(&q);break;        case 2:dequeue(&q);break;        case 3:print(&q);break;        case 4:exit(0);        }    } }

OUTPUT:

1 LILLLULUI TUHPL D:\My DS LAB>gcc CIRCULAR_QUEUE_USING_ARRAYS.C D:\My DS LAB>a ....CIRCULAR QUEUE PROGRAM USING ARRAYS... ....1. ENQUEUE 2.DEQUEUE 3.PRINT 4.EXIT .... Enter your choice :1 ....ENTER AN ELEMENT 10 .... ELEMENT ENQUEUED SUCCESSFULLY 3.PRINT 4. EXIT ....1. ENQUEUE 2.DEQUEUE .... Enter your choice : 1 ....ENTER AN ELEMENT 20 .... ELEMENT ENQUEUED SUCCESSFULLY 3.PRINT 4. EXIT ....1. ENQUEUE 2.DEQUEUE ....Enter your choice :1 ....ENTER AN ELEMENT 30 ....ELEMENT ENQUEUED SUCCESSFULLY 3.PRINT 4. EXIT ....1. ENQUEUE 2.DEQUEUE .... Enter your choice :3 ....ELEMENTS IN THE QUEUE ARE 10 20 30 ....1. ENQUEUE 2.DEQUEUE .... Enter your choice :1 3.PRINT 4.EXIT .... ENTER AN ELEMENT 40 ....ELEMENT ENQUEUED SUCCESSFULLY 3.PRINT 4. EXIT ....1. ENQUEUE 2.DEQUEUE ....Enter your choice :3

....ELEMENTS IN THE QUEUE ARE 10 20 30 ....1. ENQUEUE 2.DEQUEUE . . . . Enter your choice : 2 40 3.PRINT 4. EXIT .... THE REMOVED ELEMENT IS 10 3.PRINT 4.EXIT ....1. ENQUEUE 2.DEQUEUE .... Enter your choice :4

(b)

If we implemented the circular queue using the linked list the time complexity and space complexcity of enqueue is same until the array is full ,when the array is full we need to reallocate the array.The time and space complexity of dequeue is same in both cases