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Unit 5 dsa QUEUE
The document discusses different implementations of queues using arrays and linked lists, as well as circular queues which avoid issues with arrays filling up by connecting the last element to the first. It covers common queue operations and describes how queues are widely used in applications like operating systems, databases, and simulations for tasks like job scheduling where elements need to be processed in a first-in, first-out order. Circular queues are presented as an efficient approach to implement queues using arrays without capacity issues.
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Unit 5 dsa QUEUE
- 1. Pune Vidyarthi Griha’s COLLEGEOF ENGINEERING, NASHIK – 3. “QUEUE” By Prof. Anand N. Gharu (Assistant Professor) PVGCOE Computer Dept. 01 August 2019 .
- 2. Introduction of Queue ➢“A queue is an ordered list in which all insertions are done at one end, called rear and deletions at another end called front“ ➢ Queue when implemented using arrays has some drawbacks which can be avoided by circular queue ➢ Queue is used in many applications such as as simulation, priority queue, job queueetc
- 3. Introduction of Queue ➢One of the most common dataprocessing structures ➢ Frequently used in most of the system software's like operating systems, Network and Database implementations and in many more other areas ➢ Very useful in time-sharing and distributed computer systems where many widely distributed users share the system simultaneously
- 4. Array representation and implementationof queue ➢ An array representation of queue require three entities : 1. An array to hold queue element 2. A variable to hold index of the front element 3. A variable to hold index of the rear element
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- 8. Operation on queue implementedusing array
- 9. Operation on queue implementedusing array
- 10. Operation on queue implementedusing array
- 11. Operation on queue implementedusing array
- 12. Operation on queue implementedusing array
- 13. Queue as anADT ➢ Create : Create creates an empty queue, Q ➢ Add (i,Q) : Add adds the element i to the rear end of queue, Q and returns the newqueue ➢ Delete (Q) : Delete takes out an element i from the ➢ front end of queue and returns the resulting queue ➢ Front(Q) : Front returns the element i which is at the front position of queue ➢ Is_Empty_Q(Q) : Is_Empty_Q returns true if queue is ➢ empty otherwise returns false
- 14. Queue as anADT
- 15. Queue as anADT
- 16. Queue as anADT
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- 22. Operation on queueimplemented using Linked list
- 23. Operation on queueimplemented using Linked list
- 24. Operation on queueimplemented using Linked list
- 25. Operation on queueimplemented using Linked list
- 26. Operation on queueimplemented using Linked list
- 27. Operation on queueimplemented using Linked list
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- 29. 6-29 Second Approach: Queueas a Circular Array • If we don't fix one end of the queue at index 0, we won't have to shift elements • Circular array is an array that conceptually loops around on itself o The last index is thought to “precede” index 0 o In an array whose last index is n, the location “before” index 0 is index n; the location “after” index n is index 0 • Need to keep track of where the front as well as the rear of the queue are at any given time
- 30. 6-30 Conceptual Example ofa Circular Queue 1 0 12 11 10 1 0 12 11 10 1 0 12 11 10 After 7 enqueues front rear After 5 dequeues front rear After 8 more enqueues front rear
- 31. 6-31 Implementation of a Queue rear front 5 queue count 8 3 0 1 23 4 5 6 7 8 9 10 n-1 n-2 n-3 . .. cq
- 32. 6-32 A Queue Straddlingthe End of a Circular Array rear front 4 queue count 2 98 0 1 2 3 4 5 6 7 8 9 10 99 98 97 . .. cq
- 33. 6-33 Circular Queue Drawn Linearly rear front 4 queue count 2 98 04321 96 97 98 99 … Queue from previous slide cq
- 34. 6-34 Circular Array Implementation • Whenan element is enqueued, the value of rear is incremented • But it must take into account the need to loop back to index 0: rear = (rear+1) % queue.length; • Can this array implementation also reach capacity?
- 35. 6-35 Example: array oflength 4 What happens? rear front 3 queue count 1 2 0 321 rear front 4 queue count 2 2 0 321 Suppose we try to add one more item to a queue implemented by an array of length 4 cq cq The queue is now full. How can you tell?
- 36. 6-36 Need to expand capacity… rear front 4 queue count 2 2 0321 rear front 4 queue count 2 2 0 321 4 765 We can’t just double the size of the array and copy values to the same positions as before: circular properties of the queue will be lost These locations should be in use cq cq
- 37. 6-37 rear front 4 queue count 6 2 0 321 4765 We could build the new array, and copy the queue elements into contiguous locations beginning at location front: cq
- 38. 6-38 rear front 4 queue count 4 0 0 321 4765 Better: copy the queue elements in order to the beginning of the new array cq
- 39. 6-39 rear front 5 queue count 5 0 0 321 4765 New element is added at rear = (rear+1) % queue.length See expandCapacity() in CircularArrayQueue.java cq
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- 48. Implementation of DeQueueusing linked list
- 49. C function fordeque using circular array
- 50. C function fordeque using circular array
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- 52. Priority Queue asan ADT
- 53. Priority Queue asan ADT
- 54. Multiple Queue usingarray
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