1. CS1020 Week 9: 19 th March 2015

2. Contents  Practice Exercise 33  Practice Exercise 34  Take-home Lab #4 Week 92

3. Practice Exercise #33 QuickEat – Queue Implementation Week 93

4. QuickEat (1/3) Week 9  Problem:  The food is to be served to customers on first-come-first- serve basis  The dishes are served only when ready  There are a limited amount of dishes  Dishes Ready but No Order  Throw Away !!  4

5. QuickEat (2/3) Week 9 Dish1 Tag Dish 2 Tag Dish 3 Tag Each Dish Has Own Queue Maintain ArrayList Of Dish Queues Add More Dishes 5

6. QuickEat (3/3) Week 9  Solution :  For Each Dish – maintain a queue for the Orders  Process the Input correctly : Order (#Tag) (#DishOrdered) (#DishId) ….. Ready (#DishId)  For every order operation add to queue  For every ready operation process the queue and serve to customer 6

7. Understand Question Week 9  Things to take note:  Queue is an interface, not a class  cannot be instantiated  Maintain an arraylist for queue of all dishes  Use LinkedList class which has implementation of methods in Queue interface dishQueues.add(new LinkedList ());  Queue Operation  Use only methods in LinkedList class that are legal for Queue Eg – isEmpty(), offer(), poll() 7

8. Practice Exercise #34 WebBrowser – Stack Implementation Week 98

9. WebBrowser (1/4) Week 9  Problem:  Maintain the browsing history of User  User can move through the list websites viewed by “BACKWRD” and “FORWARD” commands  Store every new website visited in the browsing history  Print the final browsing history earliest  latest page as well as the current page 9

10. WebBrowser (2/4) Week 9 Page Backward StackForward Stack Current Page Current Page changes to recently visited URL Back Operation – Pop back stack – modify current Forward Operation – Pop forward stack – modify current 10

11. WebBrowser (3/4) Week 9  Solution :  Maintain two separate stacks – Back And Forward  Check for corner case – when first page loads  Empty Forward Stack for each new page load  “BACKWARD” – Pop from back stack  move current forward  “FORWARD” – Pop from forward stack  move current backward  Print – Earliest to Latest page history Also print the current page 11

12. WebBrowser (4/4) Week 9  Things to take note:  Make use of Java Stack API  Alternatively, solution can be achieved using LinkedList ADT  Can try it to have practice on LinkedList  Familiarize with Stack API to prepare better for SitIn Lab 3 12

13. Take-home Lab #4 Exercise 1 – Cargo Optimization Week 913

14. Cargo Optimization (1/3) Week 9  Problem:  Containers arrives at the terminal in a random order, addressed to different destination ships (A-Z)  They need to be stacked at the terminal  The destination ships arrives at the terminal in a fixed sequence (A-Z) 14

15. Terminal Cargo Optimization (2/3) Week 9 Random order To: C To: A To: D To: B 15

16. Cargo Optimization (3/3) Week 9 Terminal Fixed order 16

17. Required Solution Week 9  Minimally, how many stacks are needed, such that destination ship has all its cargo is at the top when it arrives?  Hint:  You should stack container #1 on top of another container #2 only if Container #1’s ship arrive before or at the same time as container #2  You should always choose the stack whose top container’s ship’s arrival time is closest with the new container’s ship’s arrival time 17

18. Take-home Lab #4 Exercise 2 – Queue Simulation Week 918

19.  Objective is to find the final queue resulting from VIP customers and Regular Customers in Queue and find the number of customers before the specified customer  Solution  Always insert a VIP customer before a regular customer in the queue  Redirect the links during insertion is a pre-requisite  Queue is always first come first serve. This questions requires a modified priority queue. Queue Simulation Week 919

20. Queue Visualization (VIP customer enters the Queue) (1/4) QueueSimulation VIP 1 Reg 2Reg 3Reg 1 head First VIP Customer Arrived: Week 920

21. Queue Visualization (VIP customer enters the Queue) (2/4) QueueSimulation VIP 1 Reg 2Reg 3Reg 1 head Week 921

22. Queue Visualization (VIP customer enters the Queue) (3/4) QueueSimulation VIP 1 Reg 2Reg 3Reg 1 head VIP 2 VIP 2 customers arrived: Week 922

23. Queue Visualization (VIP customer enters the Queue) (4/4) QueueSimulation VIP 1 Reg 2Reg 3Reg 1 head VIP 2 Week 923

24. Recap  Take Home Lab 4 Due: 10pm - 20 th March  Familiarize with Stack and Queue API  Question?? Week 924

25. END OF FILE Week 925