The document discusses the concept of circular queues and their implementation using arrays. It explains how to manage the rear index to allow for wrapping around the array, ensuring the queue can accommodate more elements. Methods for determining when the queue is empty or full are also highlighted, including using a counter or comparing front and rear indices.

1. Circular Queues and
Implementation with Array

2. Array Implementation
2
5 4 6 7 8 7 6
0 1 2 3 4 5 6 7 8
Front=0
Rear=6
8 7 6
0 1 2 3 4 5 6 7 8
Front=4
Rear=6
7 6 12 67
0 1 2 3 4 5 6 7 8
Front=5
Rear=8
How can we insert more elements? Rear index can
not move beyond the last element….

3. Solution: Using circular queue
 Allow rear to wrap around the array.
if(rear == queueSize-1)
rear = 0;
else
rear++;
 Or use modulo arithmetic
rear = (rear + 1) % queueSize;
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4. Enqueing in a Circular Queue
4
7 6 12 67
0 1 2 3 4 5 6 7 8
Front=5
Rear=8
Enqueue 39 Rear=(Rear+1) mod Queue Size = (8+1) mod 9 = 0
39 7 6 12 67
0 1 2 3 4 5 6 7 8
Front=5
Rear=0

5. 5
EMPTY QUEUE
[2] [3] [2] [3]
[1] [4] [1] [4]
[0] [5] [0] [5]
front = 0 front = 0
rear = 0 rear = 3
J2
J1
J3
Implementation 2: Wrapped Configuration
Can be seen as a circular queue

6. How to determine empty and full
Queues?
6
FULL QUEUE FULL QUEUE
[2] [3] [2] [3]
[1] [4][1] [4]
[0] [5] [0] [5]
front =0
rear = 5
front =4
rear =3
J2 J3
J1 J4
J5 J6 J5
J7
J8 J9
Leave one empty
space when queue
is full
Why?
How to test when queue is empty?
How to test when queue is full?

7. How to determine empty and full
Queues?
 Number of approaches
A counter indicating number of values in the
queue can be used (We will use this
approach)
Comparing the Rear and the Front of the
Queue
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