CSE1303 Part A Data Structures and Algorithms Lecture A4 – Basic Data Structures – Continued (Queues)

1. CSE1303 Part AData Structures and AlgorithmsLecture A4 – Basic Data Structures – Continued (Queues)

2. Basic Data Structures • Stacks • Queues • Lists

3. Overview • What is a Queue? • Queue Operations. • Applications. • Linear Implementation. • Circular Implementation.

4. Before Front Rear After Front Rear Append

5. Before Front Rear After This comes off the queue Rear Front Serve

6. Operations • Initialize the queue. • Append an item to the rear of the queue. • Serve an item from the front of the queue. • Is the queue empty? • Is the queue full? • What size is the queue?

7. Applications • In operating systems, e.g. printer queues, process queues, etc. • Simulation programs. • Algorithms.

8. Linear Implementation 0 1 2 3 4 5 6 7 dog fish duck cat finch Rear Front

9. Append snake 0 1 2 3 4 5 6 7 dog fish duck cat finch snake Front Rear

10. Append eel 0 1 2 3 4 5 6 7 dog fish duck cat finch snake eel Front Rear

11. Serve 0 1 2 3 4 5 6 7 fish duck cat finch snake eel Front Rear dog This comes off the queue

12. Serve 0 1 2 3 4 5 6 7 duck cat finch snake eel Rear Front fish This comes off the queue

13. Append tiger 0 1 2 3 4 5 6 7 duck cat finch snake eel tiger Front Rear

14. ROOM HERE NO ROOM HERE Append ape 0 1 2 3 4 5 6 7 duck cat finch snake eel tiger Front Rear

15. Circular Implementation 0 7 6 1 5 2 4 3

16. Circular Implementation Append ape 0 1 2 3 4 5 6 7 ape duck cat finch snake eel tiger Rear Front

17. Queue: #define MAXQUEUE 20 struct QueueRec { int count; int front; int rear; float entry[MAXQUEUE]; }; typedef struct QueueRec Queue; count: front: rear: entry: . . .

18. #ifndef QUEUEH #define QUEUEH #include <stdbool.h> #define MAXQUEUE 20 struct QueueRec { int count; int front; int rear; float entry[MAXQUEUE]; }; typedef struct QueueRec Queue; void intializeQueue(Queue* queuePtr); bool queueEmpty(const Queue* queuePtr); bool queueFull(const Queue* queuePtr); void append(Queue* queuePtr, float item); float serve(Queue* queuePtr); #endif

19. #include <stdio.h> #include <stdlib.h> #include “queue.h” void initializeQueue(Queue* queuePtr) { queuePtr -> count = 0; queuePtr -> front = 0; queuePtr -> rear = MAXQUEUE-1; } Queue: 0 count: 0 front: queuePtr: addr ofQueue 19 rear: entry: . . . 19

20. bool queueEmpty(const Queue* queuePtr) { if (queuePtr->count <= 0) { return true; } else { return false; } } bool queueFull(Queue* queuePtr) { if (queuePtr->count >= MAXQUEUE) { return true; } else { return false; } } 20

21. void append(Queue* queuePtr, float item) { if (queueFull(queuePtr)) { fprintf(stderr, “Queue is full\n”); exit(1); } else { queuePtr->rear++; if (queuePtr->rear == MAXQUEUE) { queuePtr->rear = 0; } queuePtr->entry[queuePtr->rear] = item; queuePtr->count++; } } 21

22. float serve(Queue* queuePtr) { float item; if (queueEmpty(queuePtr)) { fprintf(stderr, “Queue is empty\n”); exit(1); } else { item = queuePtr->entry[queuePtr->front]; queuePtr->front++; if (queuePtr->front == MAXQUEUE) { queuePtr->front = 0; } queuePtr->count--; } return item; } 22

23. Revision Revision: Reading • Queue • Main Operations • Implementation. • Kruse: Chapter 4.1 to 4.2 • Deitel & Deitel: Chapter 12.6 • Standish: Chapter 7 • Langsam: Chapter 4.1 Preparation • Next lecture:Lists • Kruse 4.5, 4.6, 4.8 • Deitel & Deitel (2e) 12.1, 12.2, 12.4