![OPERATIONS AND ALGORITHMS OF CIRCULAR QUEUE:
1. Insert Operation:
Step 1: [Check for the Overflow]
If front = 1 and rear = n
Output “Overflow” and return
Step 2: [Insert element in the queue.]
Else if front = 0
front = 1
rear = 1
Q [rear] = value
Step 3: [Check if the rear at the end of the queue]
Else if rear = n
rear = 1
Q [rear] = value
Step 4: [insert the element]
Else
Rear = rear + 1
Q [rear] = value
Step 5: return](https://image.slidesharecdn.com/queue-150921100809-lva1-app6891/85/Queue-7-320.jpg)
![2. Delete Operation:
Step 1: [Check for underflow]
If front = 0
Output “Underflow” and return
Step 2: [Remove the element]
Value = Q [front]
Step 3: [Check whether the queue is empty or not]
If front = rear
front = 0
rear = 0
Step 4: [Check the front pointer position]
Else if front = n
front = 1
Else
front = front + 1
Step 5: [Return the removed element]
Return [value]](https://image.slidesharecdn.com/queue-150921100809-lva1-app6891/85/Queue-8-320.jpg)
Queue
- 1. 5.Queue
- 2. Definition of Queue • A Queue is an ordered collection of items in which items are deleted from one end called the front and items are inserted from other end called rear. • The elements are inserted and deleted in FIFO manner. Front=-1 , Rear=-1 Queue
- 3. Types of Queue 1. Circular Queue. 2. Priority Queue. 3. DeQue
- 4. 4 Drawback of Linear Queue • Once the queue is full, even though few elements from the front are deleted and some occupied space is relieved, it is not possible to add anymore new elements, as the rear has already reached the Queue’s rear most position. Circular Queue • This queue is not linear but circular. • Its structure can be like the following figure: Figure: Circular Queue having Rear = 5 and Front = 0 • In circular queue, once the Queue is full the "First" element of the Queue becomes the "Rear" most element, if and only if the "Front" has moved forward. otherwise it will again be a "Queue overflow" state.
- 5. 5 Example: Consider the following circular queue with N = 5. 1. Initially, Rear = 0, Front = 0. 2. Insert 10, Rear = 1, Front = 1. 3. Insert 50, Rear = 2, Front = 1. 4. Insert 20, Rear = 3, Front = 0. 5. Insert 70, Rear = 4, Front = 1. 6. Delete front, Rear = 4, Front = 2. Rear Rear Rear Rear Rear Front Front Front Front Front Front=0 Rear=0
- 6. 6 7. Insert 100, Rear = 5, Front = 2. 8. Insert 40, Rear = 1, Front = 2. 9. Insert 140, Rear = 1, Front = 2. As Front = Rear + 1, so Queue overflow. 10. Delete front, Rear = 1, Front = 3. Front Rear FrontRear Rear Rear Front Front 11. Delete front, Rear = 1, Front = 4. 12. Delete front, Rear = 1, Front = 5. Rear Rear Front Front
- 7. OPERATIONS AND ALGORITHMS OF CIRCULAR QUEUE: 1. Insert Operation: Step 1: [Check for the Overflow] If front = 1 and rear = n Output “Overflow” and return Step 2: [Insert element in the queue.] Else if front = 0 front = 1 rear = 1 Q [rear] = value Step 3: [Check if the rear at the end of the queue] Else if rear = n rear = 1 Q [rear] = value Step 4: [insert the element] Else Rear = rear + 1 Q [rear] = value Step 5: return
- 8. 2. Delete Operation: Step 1: [Check for underflow] If front = 0 Output “Underflow” and return Step 2: [Remove the element] Value = Q [front] Step 3: [Check whether the queue is empty or not] If front = rear front = 0 rear = 0 Step 4: [Check the front pointer position] Else if front = n front = 1 Else front = front + 1 Step 5: [Return the removed element] Return [value]
- 9. Priority Queues • A Priority queue is a collection of elements where each elements is assigned a priority. 1. An element of higher priority is processed first. 2. Two elements with the same priority are processed according to the order in which they are added to queue. e.g. Job Scheduling by OS.
- 10. • But should follow the FIFO concept. • It can be a Ascending priority Queue or Descending priority queue.
- 11. DEQues (Double Ended Queue) • A Deque is a queue in which elements can be inserted or deleted from any end. but not in the middle. • Four operations are possible on Deque. 1. Insert from front. 2. Insert from rear. 3. Delete from Front. 4. Delete from rear.
- 12. Reversing a stack using queue 1. Pop value from the stack. 2. Add that value to the queue. 3. Repeat step 1. till stack is not empty. 4. Delete a value from the queue and push it in the same stack. 5. Repeat step 4. till queue is not empty.