how to find number of elements in a Circular Queue

Question

how do i find the number of items in a circular queue?

|front - rear| doesnt always work.

is there one equation to know how many element is in a cir

Answer 1

No of items in Circular queue is,

size = (N-f+r) mod N

where

• N is the size of array used in circular fashion
• f index of the front element
• r index immediately past the rear element

This formula work for both liner and circular queues.

Answer 2

no. of elements = (rear + MAX_SIZE - front) % MAX_SIZE + 1

Answer 3

The easiest way to count the number of elements in the circular queue is:

if front > rear(i.e. front is ahead than rear) Just count the number of empty spaces in between

front - (rear+1)

else if front < rear:

rear - front + 1

A C program if you need to:

    int find_ele(int total,int front,int rear){
         if(rear < front ) {  \\1st case
int res =    front - rear + 1;
return (total-res);}

else{
      return (rear - front + 1);
}
}

Answer 4

can your queue contain the same element in more than one location? if it can then I don't think you can do this as there is no way to know the difference between:

a->b->c

and

a->b->c->a->b->c

if it can't contain the same element more than once, just look through the queue until you find an element you have already seen

Answer 5

actually the size would be,

size = front > rear ? (MAX - front + rear + 1) : (rear - front + 1);

or one can go for a generic formula:

size = abs(abs(MAX - front) - abs(MAX -rear));//this works in every situation

Answer 6

if (Cqueue_front>Cqueue_rear) cout<<" The number of queue items are : "<