1. Stacks and Queues

2. Not really data structures – More of an enforcement of policy – Can be implemented using an array or linked list – Can store just about any kind of data Queues – First In, First Out (FIFO) – Like waiting in line Stacks – First In, Last Out (FILO) – Like a stack of trays Stacks and Queues

3. Stacks Three primary operations – Push() – put new data on the top of the stack – Pop() – remove data from the top of the stack – Peek() – get a copy of the data on the top of the stack Useful – our function stack! – stack of cards, tiles, loot, etc…

4. Example (pushing) 5 Note: could use a linked list also

5. Example (pushing) 5 11

6. Example (pushing) 5 11 -6

7. Example (pushing) 5 11 -6 45

8. Example (current stack) 5 11 -6 45

9. Example (peeking) 5 11 -6 45

10. Example (popping) 5 11 -6 45

11. Example (pushing) 5 11 -6 31

12. Example (popping) 5 11 -6 31

13. Example (popping) 5 11 -6

14. Example (popping) 5 11

15. Example (popping) 5 FILO

16. Queues Two primary operations – Enqueue() – put new data at the end of the queue – Dequeue() – remove data from the beginning of the queue – Peek() – yes, its still there… Useful – Enforcing fairness (waitlist at SPSU) – Player turns during a round

17. Example

18. Example (enqueue a 5) 5

19. Example 5

20. Example (enqueue an 11) 5 11

21. Example 511

22. Example (enqueue a -6) 511 -6

23. Example 511 -6

24. Example (dequeue) 511 -6

25. Example (dequeue) 511 -6

26. Example (dequeue) 5 11 -6 FIFO

27. Example (dequeue) 11 -6

28. Not really data structures – More of an enforcement of policy – Can be implemented using an array or linked list Queues are FIFO Stacks are FILO Which data structure is LILO? Which one is LIFO? Summary