meljun cortes data structures queues

Data Structures

� Queue - an ordered list

� Top/rear – end of the list where all insertion

takes place

� Bottom/front – other end of the list where all

deletions take place

� This type of processing behavior is called FIFO

� With stack, only one element is "visible" at a

given time, while on queue, the "visible” element

Queue

Queues *Property of STI of21

given time, while on queue, the "visible” element

will always be the one at the bottom of the

queue

Data Structures

� Queue as one-dimensional array

Representation of Queues


� Queues are represented as one-dimensional

arrays when:

� The maximum size of the queue is known.

� The amount of time wasted in shifting the

elements after deletion is negligible.

Data Structures

� Queue as Singly-linked list

� when the maximum size of the queue is

unknown.

Representation of Queues


Data Structures

Operations on Queue

Arrays Stacks Queues

Insert Push Put, add, enqueue

Delete POP Delete, get, dequeue

Search Peek Peek, retrieve


� Enqueue - always at the top of the list

Data Structures

� Dequeue - delete at the bottom of the list

� Peek or Retrieve - print or display the element

at the bottom of the list

� being viewed or retrieve is what you are

about to delete or remove and not what you

have inserted

� Empty and Full

Operations on Queue


� Empty and Full

� return you an error because the queue is

empty

� a message that the queue is full when trying

to insert another element

Data Structures

� Sometimes called as ring buffer

� elements of the array are “arranged” in a

circular manner

Circular Queue


Data Structures

� Initially, top and bottom contain the value zero

(0)

� Insert element “A”, top and bottom will be = 1

Circular Queue


Data Structures

� Insert element “B”, bottom = 1 and top = 2

Circular Queue


Data Structures

� Delete bottom element “A”

Circular Queue


Data Structures

Circular Queue

� Algorithm for inserting element in a circular

queue:

1. If bottom of the queue is pointing to the last

position then proceed to second or else

third step

2. make the bottom value as 0

3. increment the bottom value by one

4. a. if the top points where bottom is pointing

and the queue holds a not NULL value for


and the queue holds a not NULL value for

it, then its a "queue overflow" state, so quit;

else go to step-b

b. insert the new value for the queue

position pointed by the bottom

Data Structures

Circular Queue

{

if(bottom == maxSize -1)

bottom = -1;

queArray[++bottom] = j;

nItems++;

}

� Top = Bottom = 0


� insert “A” into the queue


� additional 9 insertions with no deletion is done

� Top = 10

� Bottom = 1

Data Structures

Circular Queue

� algorithm to delete the element at the top of a

circular queue

1. If the queue is empty then say "empty queue"

and quit; else continue

2. Delete the top element

3. If the top is pointing to the last position of the

queue then step-4 else step-5

4. Make the top point to the first position in the

queue and quit

5. Increment the top position by one


5. Increment the top position by one

{

int temp = queArray[top++];

if(top== maxSize)

Top = 0;

nItems--;

return temp;

}

Data Structures

Java Code for Queue

public void insert(int j)

{

if(rear == maxSize -1)

rear = -1;

queArray[++rear] = j;

nItems++;

}

------------------------------------

public int remove()


public int remove()

{

int temp = queArray[front++];

if(front == maxSize)

front = 0;

nItems--;

return temp;

}

-----------------------------------

public int peekFront()

{

return queArray[front];

}

Data Structures

Priority Queue

� special type of queue where elements in this

queue are ordered, in an ascending or

descending manner

� Operations on Priority Queue

� Insert

� Delete

� Peek and new


Priority queue insertion

Priority queue deletion

Data Structures

Priority Queue

� inserting an item

public void insert(double item)

{

int j;

if(nItems==0)

queArray[nItems++] = item;

else

{


{

for(j=nItems-1; j>=0; j--)

{

if(item>queArray[j])

queArray[j+1] =

queArray[j];

else

break;

}

queArray[j+1] = item;

nItems++;

}

}

Data Structures

Priority Queue

� model of the memory allocation is described in

terms of three (3) queues: the Arrival Queue,

the Execution Queue, and the Memory Queue

� Arrival Queue is a strict FIFO queue

� Data field of each node in the Memory Queue

will be subdivided into a pair of fields

� MemAddr, is a memory address

� MemSize, is the size of contiguous memory


� MemSize, is the size of contiguous memory

� Execution Queue, will be used to monitor the

execution of jobs

Data Structures

Priority Queue

� Data field of each node in the Execution Queue

� For Arrival queue


� Represented as Singly-Linked List Nodes:

� As One-Dimensional Array Elements:

Data Structures

Simulation of Model

� Memory Queue

� Execution Queue


� Arrival Queue

Data Structures

Simulation of Model

� Arrival Queue



� Memory Queue

Data Structures

Simulation of Model

� Execution Queue


� Contents of Queue

Data Structures

Abstract Data Type

� way of looking a data structure on what it does

in a program and not how it does it

� Data Type

� int and double which is applied to built-in

types

� Abstraction

a mechanism and practice to reduce and


� a mechanism and practice to reduce and

factor out details so that one can focus on a

few concepts at a time

� Interface

� specification of ADT

� Abstract Data Type

� kind of data abstraction where a type's

internal form is hidden behind a set of

access functions

meljun cortes data structures queues

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