CS1020
Week 9: 19th March 2015
Contents
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Practice Exercise 33
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Practice Exercise 34
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Take-home Lab #4
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Week 9
Practice Exercise #33
QuickEat – Queue Implementation
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Week 9
QuickEat (1/3)
Problem:
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The food is to be served to customers on first-come-firstserve basis
The dishes are served only when ready
There are a limited amount of dishes
Dishes Ready but No Order  Throw Away !! 
Week 9
QuickEat (2/3)
Each Dish Has Own Queue
Maintain
ArrayList Of
Dish Queues
Dish1
Tag
Tag
Dish 2
Tag
Tag
Dish 3
Tag
Tag
Add More Dishes
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Week 9
QuickEat (3/3)
Solution :
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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
Week 9
Understand Question
Things to take note:
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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<Integer>());
Queue Operation  Use only methods in LinkedList class
that are legal for Queue
Eg – isEmpty(), offer(), poll()
Week 9
Practice Exercise #34
WebBrowser – Stack Implementation
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Week 9
WebBrowser (1/4)
Problem:
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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
Week 9
WebBrowser (2/4)
Back Operation – Pop
back stack – modify
current
Forward Operation –
Pop forward stack –
modify current
Current Page
Page
Page
Page
Current Page changes
to recently visited
URL
Page
Page
Backward Stack
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Page
Forward Stack
Week 9
WebBrowser (3/4)
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Solution :
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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
Week 9
WebBrowser (4/4)
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Things to take note:
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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
Week 9
Take-home Lab #4
Exercise 1 – Cargo Optimization
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Week 9
Cargo Optimization (1/3)
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Problem:
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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)
Week 9
Cargo Optimization (2/3)
To: B
Random
order
To: D
To: A
Terminal
To: C
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Week 9
Cargo Optimization (3/3)
Fixed
order
Terminal
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Week 9
Required Solution
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Minimally, how many stacks are needed, such that
destination ship has all its cargo is at the top when it
arrives?
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Hint:
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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
Week 9
Take-home Lab #4
Exercise 2 – Queue Simulation
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Week 9
Queue
Simulation
Queue Simulation
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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
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Solution
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Always insert a VIP customer before a regular
customer in the queue
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Redirect the links during insertion is a pre-requisite
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Queue is always first come first serve. This
questions requires a modified priority queue.
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Week 9
head
Reg 1
Reg 2
Reg 3
First VIP Customer Arrived:
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VIP 1
Week 9
Queue
Simulation
Queue Visualization (VIP customer
enters the Queue) (1/4)
Reg 1
head
Reg 2
Reg 3
VIP 1
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Week 9
Queue
Simulation
Queue Visualization (VIP customer
enters the Queue) (2/4)
Reg 1
head
Reg 2
Reg 3
VIP 1
VIP 2 customers arrived:
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VIP 2
Week 9
Queue
Simulation
Queue Visualization (VIP customer
enters the Queue) (3/4)
Reg 1
head
VIP 1
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Reg 2
VIP 2
Week 9
Reg 3
Queue
Simulation
Queue Visualization (VIP customer
enters the Queue) (4/4)
Recap
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Take Home Lab 4
Due: 10pm - 20th March
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Familiarize with Stack and Queue API
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Question??
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Week 9
END OF FILE
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Week 9