Exactly !!! I also solved it in the same way but the answer given is 91.
This is what they have mentioned in the explanation :
”In the question, it is mentioned that we have and arrange ranging from index 0 to 99 and the size of the queue is 100, for a circular queue there are two possible implementations, one is with array size n and queue size n and another with array size n and queue size n-1, in the first case the tail/rear points to the element last inserted and not the location to insert the next element. Hope it is clear, with this in mind the number of elements which are in the circular queue is 91.”
As far as I understood from this explanation they are also solving it in the same way but i don’t know how their answer is coming out to be 91. May be they are also including the element pointed by FRONT, but what i have studied is that first we increment the FRONT pointer and then delete the element pointed by it. So the element pointed by FRONT should not be considered.
Please do mention if you can understand something different from their explanation.