queue operations performed on queue queue applications Example to enqueue Algorithm To enqueue() / add () An Element (ITEM )In The Queue Example to dequeue Algorithm To dequeue() / remove() An Element (ITEM )In The Queue PRIORITY Queue PRIORITY Queue Representation

1. Chapter 5Chapter 5
queuesqueues
01/31/18 BY MS. SHAISTA QADIR 1
PRESENTED BY
Shaista Qadir
Lecturer king khalid university

2. CONteNtsCONteNts
 queue
 OperatiONs perfOrmed ON queue
 queue appliCatiONs
 example tO eNqueue
 algOrithm tO enqueue() / add () aN elemeNt
(item )iN the queue
 example tO dequeue
 algOrithm tO dequeue() / remove() aN elemeNt
(item )iN the queue
 priOritY queue
 priOritY queue represeNtatiON
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3. queuequeue
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 A queue is simply a waiting line that grows by adding
elements to its end and shrinks by taking elements from its
front.
 Unlike a stack, a queue is a structure in which both ends
are used.
 one for adding new elements and one for removing them.
 Therefore, the last element has to wait until all elements
preceding it on the queue are removed.
 A queue is an FIFO structure: first in/first out.

4. OperatiONs perfOrmed ONOperatiONs perfOrmed ON
queuequeue
01/31/18 BY MS. SHAISTA QADIR 4
 Queue operations are similar to stack operations. The
following operations are needed to properly manage a
queue:
 clear() : Clear the queue.
 isEmpty() : Check to see if the queue is empty.
 enqueue(el): Put the element el at the end of the queue.
 dequeue() : Take the first element from the queue.
 firstEl() : Return the first element in the queue without
removing it.

5. operations performed onoperations performed on
QUeUeQUeUe
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 A series of enqueue and dequeue operations is shown in Figure .
 This time—unlike for stacks—the changes have to be monitored
both at the beginning of the queue and at the end.
 The elements are enqueued on one end and dequeued from the
other.
 For example, after enqueuing 10 and then 5, the dequeue
operation removes 10 from the queue

6. QUeUe applicationsQUeUe applications
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APPLICATIONS OF QUEUE:
◦ Waiting Line
◦ Access to Shared recourses (Example: Printer)
◦ Multiprogramming
◦ Client-Server system

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 Example: FOR enqueue() / add()
 array size is 8,
 therefore, the index of the array will be from 0 to 7.
 Elements inside array are 1, 7, 5 and 2
 When we enqueue(6), 6 has been inserted in the queue.
 Now, the rear index is containing 4 while the front has the
same 0 index.
example to enQUeUeexample to enQUeUe

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 Example: FOR enqueue() / add()
 When we enqueue(8) another element 8 is inserted in the
queue.
example to enQUeUeexample to enQUeUe

9. Algorithm toAlgorithm to enqueue() / add ()enqueue() / add ()
An ElEmEnt (itEm )in thEAn ElEmEnt (itEm )in thE
QuEuEQuEuE
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Algorithm To enqueue() / add () An Element (ITEM )In The
Queue:
1. If (REAR == max) Then
2. Print: Overflow
3. Else
4. If (FRONT and REAR == 0) Then
(a) Set FRONT = 1
(b) Set REAR = 1
5. Else
6. Set REAR = REAR + 1 [End of Step 4 If]
7. QUEUE[REAR] = ITEM
8. Print: ITEM inserted [End of Step 1 If]
9. Exit

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PROGRAM LOGIC:
void enqueue(int j)
{
if(rear == maxsize-1)
rear = -1;
qarr[++rear] = j;
cnt++;
}
Algorithm toAlgorithm to enqueue() / add ()enqueue() / add ()
An ElEmEnt (itEm )in thEAn ElEmEnt (itEm )in thE
QuEuEQuEuE

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 Example To dequeue ()/ remove () an element from
queue.
 Element is deleted from front end.
 After a call of dequeue() method:
 Another call of dequeue() method:
ExAmplE to dEQuEuEExAmplE to dEQuEuE

12. Algorithm toAlgorithm to dequeue() / remove()dequeue() / remove()
An ElEmEnt (itEm )in thEAn ElEmEnt (itEm )in thE
QuEuEQuEuE
01/31/18 BY MS. SHAISTA QADIR 12
Algorithm to dequeue()/ remove () an element (ITEM )
from the queue:
1. If (FRONT == 0) Then
2. Print: Underflow // Check for underflow
3. Else
4. ITEM = QUEUE[FRONT]
5. If (FRONT == REAR) Then // Check if only one element in Queue
(a) Set FRONT = 0
(b) Set REAR = 0
6. Else
7. Set FRONT = FRONT + 1 [End of Step 5 If]
8. Print: ITEM deleted [End of Step 1 If]
9. Exit

13. Algorithm toAlgorithm to dequeue() / remove()dequeue() / remove()
An ElEmEnt (itEm )in thEAn ElEmEnt (itEm )in thE
QuEuEQuEuE
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PROGRAM LOGIC:
int dequeue()
{
int temp = qarr[front];
front++;
if(front == maxsize)
front = 0;
cnt--;
return temp;
}

14. PrioritY QuEuEPrioritY QuEuE
01/31/18 BY MS. SHAISTA QADIR 14
• In many situations, simple queues are inadequate, as when
first in/first out scheduling has to be overruled using some
priority criteria.
• In a post office example, a handicapped person may have
priority over others.
• Therefore, when a clerk is available, a handicapped person is
served instead of someone from the front of the queue.
• In a sequence of processes, process P2 may need to be
executed before process P1 for the proper functioning of a
system, even though P1 was put on the queue of waiting
processes before P2.
• In situations like these, a modified queue, or priority queue,
is needed. In priority queues, elements are dequeued
according to their priority and their current queue position.

15. PrioritY QuEuE rEPrEsEntAtionPrioritY QuEuE rEPrEsEntAtion
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• Priority queues can be represented by two variations of
linked lists.
• In one type of linked list, all elements are entry ordered,
• And in another, order is maintained by putting a new
element in its proper position according to its priority.
• In both cases, the total operational times are O(n)
• because, for an unordered list, adding an element is
immediate but searching is O(n),
• And in a sorted list, taking an element is immediate but
adding an element is O(n).

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THANK YOUTHANK YOU