![Queue
• Queue is Linear Data Structure
• It follows First In First Out(FIFO) principal
• It has two pointers front and rear
e.g.:
10 20 30 40 50
A[0] A[1] A[2] A[3] A[4]
Insertion
(ENQUEUE)
Deletion
(DEQUEUE)](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-2-320.jpg)
![Operations on Queue
Insertion:
Algorithm:
Step 1: If REAR = MAX – 1 then
Write “Queue is Overflow”
Goto step 4
[End of IF]
Step 2: IF FRONT=-1 and REAR=-1
SET FRONT=REAR=0
ELSE
SET REAR=REAR+1
[END OF IF]
Step 3: SET QUEUE [REAR] = NUM
Step 4: EXIT](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-3-320.jpg)
![Example of Insertion in Queue
A[0] A[1] A[2] A[3] A[4]
F=R=(-1)
10
A[0] A[1] A[2] A[3] A[4]
F=R=0
10 20
F=0 R=1
A[0] A[1] A[2] A[3] A[4]](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-4-320.jpg)
![Operations on Queue
Deletion:
Algorithm:
Step 1: IF FRONT = -1 OR FRONT>REAR
Write “Queue is Underflow”
ELSE
SET VAL=QUEUE [FRONT]
FRONT = FRONT + 1
[END OF IF]
Step 2: EXIT](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-5-320.jpg)
![Example of Deletion in Queue
10 20
A[0] A[1] A[2] A[3] A[4]
20
A[0] A[1] A[2] A[3] A[4]
F=R=1
F=0 R=1](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-6-320.jpg)
![What is Circular Queue?
• The Arrangement of the elements Q[0], Q[1],
...,Q[n] in a circular fashion with Q[1]
following Q[n] is called Circular Queue.
• The last node is connected to first node to
make a circle.
• Initially, Both Front and Rear pointers points
to the beginning of the array.
• It is also known as “Ring Buffer”.](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-10-320.jpg)
![• e.g.:
Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
F=R=Q[0]](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-11-320.jpg)
![Operations on Circular Queue
Insertion:
Algorithm:
Step 1: IF FRONT=0 and REAR=MAX-1 Then
Write “Overflow”
Goto Step 4
[END OF IF]
Step 2: IF FRONT = REAR=-1 then
SET FRONT=REAR=0
ELSE IF REAR=MAX-1 and FRONT!=0
SET REAR=0
ELSE
SET REAR=REAR+1
[END OF IF]
Step 3: SET QUEUE[REAR]=VAL
Step 4: EXIT](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-12-320.jpg)
![F=Q[0]
e.g.:
R=Q[7]
Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
5
10
1520
25
30
35 40
Queue is full(Overflow)](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-13-320.jpg)
![Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
F=R=Q[0]
e.g.:
If F=R=-1 then F=R=0
2
e.g.: (cond..)](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-14-320.jpg)
![F=Q[1]
e.g.: (cond..)
R=Q[7]Q[7]
Q[0]
Q[1]Q[2]
Q[3]
Q[4]
Q[5] Q[6]
1520
25
30
35 40
If REAR=MAX-1 and FRONT!=0
45](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-15-320.jpg)
![F=Q[0]
e.g.: (cond..)
Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
5
10
R=Q[1]
Rear=Rear+1](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-16-320.jpg)
![Operations on Circular Queue
Deletion:
Algorithm:
Step 1: If FRONT = -1 then
Write ("Circular Queue Underflow“)
GOTO Step 4
Step 2: SET VAL=QUEUE[FRONT]
Step 3: If FRONT = REAR then
SET FRONT=REAR=-1
ELSE
IF FRONT=MAX-1
SET FRONT=0
ELSE
SET FRONT=FRONT+1
[END OF IF]
[END OF IF]
Step 4: EXIT](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-17-320.jpg)
![Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
F=R=-1
e.g.:
Queue is Empty(Underflow)](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-18-320.jpg)
![Q[0]
Q[1]
Q[2]Q[3]
Q[4]
Q[5]
Q[6] Q[7]
F=R=Q[0]
e.g.:
If F=R=0 then F=R=-1
5](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-19-320.jpg)
![F=Q[1]
e.g.: (cond..)
R=Q[7]Q[7]
Q[0]
Q[1]Q[2]
Q[3]
Q[4]
Q[5] Q[6]
1520
25
30
35 40
45
If Front=MAX-1 then Front=0](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-20-320.jpg)
![F=Q[4]
e.g.: (cond..)
R=Q[1]Q[1]
Q[2]
Q[3]Q[4]
Q[5]
Q[6]
Q[7] Q[8]
20
25
30
35 40
Front=Front+1
45](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-21-320.jpg)
![Array Representation of Priority Queue
15 10
20 15 10
25 15 13 10
A[0] A[1] A[2] A[3] A[4]
Front Rear
A[0] A[1] A[2] A[3] A[4]
Front Rear
A[0] A[1] A[2] A[3] A[4]
Front Rear](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-26-320.jpg)
![Array Representation of Priority Queue
20 15 13 10
15 13 10
13 10
A[0] A[1] A[2] A[3] A[4]
Front Rear
A[0] A[1] A[2] A[3] A[4]
Front Rear
A[0] A[1] A[2] A[3] A[4]
Front Rear](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-28-320.jpg)
![Deque / Double Ended Queue
• A list in which elements can be inserted or
deleted either end
• It is also known as “Head-Tail Linked List”
• It has two pointers LEFT and RIGHT, which
point to either end of the deque.
• Dequeue can be implemented using Circular
Array or a Circular doubly linked list where
Dequeue[n-1] is followed by Dequeue[0]](https://image.slidesharecdn.com/queue-171028184435/85/Queue-in-Data-Structure-30-320.jpg)
Queue in Data Structure
- 1. Subject : Data Structures Topic : Queue
- 2. Queue • Queue is Linear Data Structure • It follows First In First Out(FIFO) principal • It has two pointers front and rear e.g.: 10 20 30 40 50 A[0] A[1] A[2] A[3] A[4] Insertion (ENQUEUE) Deletion (DEQUEUE)
- 3. Operations on Queue Insertion: Algorithm: Step 1: If REAR = MAX – 1 then Write “Queue is Overflow” Goto step 4 [End of IF] Step 2: IF FRONT=-1 and REAR=-1 SET FRONT=REAR=0 ELSE SET REAR=REAR+1 [END OF IF] Step 3: SET QUEUE [REAR] = NUM Step 4: EXIT
- 4. Example of Insertion in Queue A[0] A[1] A[2] A[3] A[4] F=R=(-1) 10 A[0] A[1] A[2] A[3] A[4] F=R=0 10 20 F=0 R=1 A[0] A[1] A[2] A[3] A[4]
- 5. Operations on Queue Deletion: Algorithm: Step 1: IF FRONT = -1 OR FRONT>REAR Write “Queue is Underflow” ELSE SET VAL=QUEUE [FRONT] FRONT = FRONT + 1 [END OF IF] Step 2: EXIT
- 6. Example of Deletion in Queue 10 20 A[0] A[1] A[2] A[3] A[4] 20 A[0] A[1] A[2] A[3] A[4] F=R=1 F=0 R=1
- 7. Types Of Queue 1. Circular Queue 2. Priority Queue 3. Deque 4. Multiple Queue
- 9. Why Circular Queue is needed? • Problem: – Wastage of memory in standard queue in DEQUEUE operation
- 10. What is Circular Queue? • The Arrangement of the elements Q[0], Q[1], ...,Q[n] in a circular fashion with Q[1] following Q[n] is called Circular Queue. • The last node is connected to first node to make a circle. • Initially, Both Front and Rear pointers points to the beginning of the array. • It is also known as “Ring Buffer”.
- 12. Operations on Circular Queue Insertion: Algorithm: Step 1: IF FRONT=0 and REAR=MAX-1 Then Write “Overflow” Goto Step 4 [END OF IF] Step 2: IF FRONT = REAR=-1 then SET FRONT=REAR=0 ELSE IF REAR=MAX-1 and FRONT!=0 SET REAR=0 ELSE SET REAR=REAR+1 [END OF IF] Step 3: SET QUEUE[REAR]=VAL Step 4: EXIT
- 13. F=Q[0] e.g.: R=Q[7] Q[0] Q[1] Q[2]Q[3] Q[4] Q[5] Q[6] Q[7] 5 10 1520 25 30 35 40 Queue is full(Overflow)
- 14. Q[0] Q[1] Q[2]Q[3] Q[4] Q[5] Q[6] Q[7] F=R=Q[0] e.g.: If F=R=-1 then F=R=0 2 e.g.: (cond..)
- 15. F=Q[1] e.g.: (cond..) R=Q[7]Q[7] Q[0] Q[1]Q[2] Q[3] Q[4] Q[5] Q[6] 1520 25 30 35 40 If REAR=MAX-1 and FRONT!=0 45
- 17. Operations on Circular Queue Deletion: Algorithm: Step 1: If FRONT = -1 then Write ("Circular Queue Underflow“) GOTO Step 4 Step 2: SET VAL=QUEUE[FRONT] Step 3: If FRONT = REAR then SET FRONT=REAR=-1 ELSE IF FRONT=MAX-1 SET FRONT=0 ELSE SET FRONT=FRONT+1 [END OF IF] [END OF IF] Step 4: EXIT
- 18. Q[0] Q[1] Q[2]Q[3] Q[4] Q[5] Q[6] Q[7] F=R=-1 e.g.: Queue is Empty(Underflow)
- 19. Q[0] Q[1] Q[2]Q[3] Q[4] Q[5] Q[6] Q[7] F=R=Q[0] e.g.: If F=R=0 then F=R=-1 5
- 20. F=Q[1] e.g.: (cond..) R=Q[7]Q[7] Q[0] Q[1]Q[2] Q[3] Q[4] Q[5] Q[6] 1520 25 30 35 40 45 If Front=MAX-1 then Front=0
- 21. F=Q[4] e.g.: (cond..) R=Q[1]Q[1] Q[2] Q[3]Q[4] Q[5] Q[6] Q[7] Q[8] 20 25 30 35 40 Front=Front+1 45
- 22. Priority Queue
- 23. Priority Queue • In priority queue, each element is assigned a priority. • Priority of an element determines the order in which the elements will be processed. • Rules: 1. An element with higher priority will processed before an element with a lower priority. 2. Two elements with the same priority are processed on a First Come First Serve basis.
- 24. Types of Priority Queue 1. Ascending Priority Queue In this type of priority queue, elements can be inserted into any order but only the smallest element can be removed. 2. Descending Priority Queue In this type of priority queue, elements can be inserted into any order but only the largest element can be removed.
- 25. Array Representation of Priority Queue Insertion Operation: • While inserting elements in priority queue we will add it at the appropriate position depending on its priority • It is inserted in such a way that the elements are always ordered either in Ascending or descending sequence
- 26. Array Representation of Priority Queue 15 10 20 15 10 25 15 13 10 A[0] A[1] A[2] A[3] A[4] Front Rear A[0] A[1] A[2] A[3] A[4] Front Rear A[0] A[1] A[2] A[3] A[4] Front Rear
- 27. Array Representation of Priority Queue Deletion Operation: • While deletion, the element at the front is always deleted.
- 28. Array Representation of Priority Queue 20 15 13 10 15 13 10 13 10 A[0] A[1] A[2] A[3] A[4] Front Rear A[0] A[1] A[2] A[3] A[4] Front Rear A[0] A[1] A[2] A[3] A[4] Front Rear
- 30. Deque / Double Ended Queue • A list in which elements can be inserted or deleted either end • It is also known as “Head-Tail Linked List” • It has two pointers LEFT and RIGHT, which point to either end of the deque. • Dequeue can be implemented using Circular Array or a Circular doubly linked list where Dequeue[n-1] is followed by Dequeue[0]
- 31. Types of Deque • Input Restricted Deque:- In this dequeue, insertion can be done only at one of the end, while deletion can be done from both ends. • Output Restricted Deque:- In this dequeue, deletion can be done only at one of the ends, while insertions can be done on both ends