Circular Queue - DSA

8/12/2019 Circular Queue - DSA

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Circular Queue - DSA


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Circular Based


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Create queue

#define MAXQUEUE 10struct queue{

int items[MAXQUEUE];

int front, rear};struct queue q;q.front, q.rear=MAXQUEUE-1;


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Empty queue

empty (pq)

struct queue pq;

{return ((pq.front==pq.rear)? TRUE:FALSE);

}


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From main()

if(empty (q))

queue is empty

Elsequeue is not empty


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Remove Operation

remove (pq)struct queue pq;{

if(empty (pq)){

printf(queue underflow);exit(1);}

if(pq.front==MAXQUEUE-1)pq.front=0;

elsepq.front++;

return (pq.items[pq.front]);}


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Insert Operationinsert (pq,x)

struct queue pq;

int x;

{

if(pq.rear==MAXQUEUE-1)

pq.rear==0;

elsepq.rear++;

if(pq.rear==pq.front)

{

printf(queue overflow);

exit(1);}

pq.items[pq.front]=x;return;

}


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Problems with Stack & Queue

Both the stack and the queue are data structureswhose elements are ordered based on the sequencein which they have been inserted.

The pop operation retrieves the last element insertedand the remove operation retrieves the first elementinserted.

If there is an intrinsic order among the elementsthemselves (for example, numeric order or alphabeticorder), it is ignored in the stack or queue operations.


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Solution: Priority Queue

The priority queue is a data structure in which

the intrinsic ordering of the element does

determine the results of its basic operations.

Types

Ascending priority queue

Descending priority queue


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Ascending priority queue

It is a collection of items into which items canbe inserted arbitrarily and from which onlythe smallest item can be removed.

If apq is an ascending order priority queue,the operation pqinsert (apq,x) inserts element

x into apq and pqmindelete (apq) removesthe minumum element from apq and returnits value.


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Descending priority queue

It is similar but allows deletion of only the largest item.

The operations applicable to a descending priority queue,dpq, are pqinsert(dpq,x)and pqmaxdelete (dpq).

pqinsert(dpq,x) inserts element x into dpq and is logicallyidentical to pqinsertfor an ascending priority queue.

pqmaxdelete(dpq) removes the maximum element fromdpq and returns its value


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empty(pq)

This operation applies to both types of priority

queue and determines whether a priority

queue is empty.

pqmindelete or pqmaxdelete can only be

applied to a nonempty priority queue.


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Conditionascending pq

Once pqmindelete has been applied to retrieve thesmallest element of an ascending priority queue, it canbe applied again to retrieve the next smallest, and soon.

Thus the operation successively retrieves the elementsof a pqin ascending order.

If a small element is inserted after several deletions,the next retrieval will return that small element, whichmay be smaller than a previously received elements.


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ConditionDescending pq

Similar to ascending pq


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Possibility

It is not that the pq will have only the number orcharacters.

It may have complex structures for example telephone-book listings consist of last names, first names,addresses and phone numbers and are ordered by lastname.

Some times it may not be even the part of the queuefor example in stack entry it may be required to view inthe form of the time of insertion.


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Array implementation of a PQ

if (pq.rear>=maxpq)

{

printf(priority queue overflow);

exit(1);

}

pq.itmes[pq.rear]=x;

pq.rear++;

Condition pq are maintained in positions 0 to n-1 of anarray pq.items of size maxpq, and suppose thatpq.rear equals the first empty array position, n.


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Problem

As the insertion keep on going no issue.

If deletion comes that is removal

pqmindelete(pq) then

Locate the smallest element that is it needs toread all the place.

How is it possible to delete in the middle? If stackand queue having the certain procedures.


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Problems

How shall we identify the free location?


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Thank You

Documents

Circular Queue - DSA