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Computer Science 320SC Programming Assignment 4

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Computer Science 320SC
Programming Assignment 4

Requirements
This fourth assignment lets you get familiar with successive improvements with algorithm design for
a concrete “real-world” problem. There are three programs required using cleaver brute-force, divideand-conquer and dynamic programming. It is worth 5% of your total course marks. Please try and test
with your own generated input cases before submitting to the automated marker.
Problem: Fibre Cabling

Description

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Computer Science 320SC
Programming Assignment 4

Requirements
This fourth assignment lets you get familiar with successive improvements with algorithm design for
a concrete “real-world” problem. There are three programs required using cleaver brute-force, divideand-conquer and dynamic programming. It is worth 5% of your total course marks. Please try and test
with your own generated input cases before submitting to the automated marker.
Problem: Fibre Cabling
A big internet infrastructure company in New Zealand has been tasked with wiring up homes with
fibre optic broadband cables. However, since this is a business for profit, not all homes will need to
be hooked up. The company Circus has asked you to help them determine which homes they should
connect cables, ready for sale. The main constraint of this problem is that if two homes on a street is
cabled then all intermediate homes on the path between them must also be, irrespective if they signup for an internet plan or not. The company makes a certain amount of profit based on which plan
customers purchase; it also losses money if a complicated connection is done without any plan purchase.
An input scenario is a sequence a1, a2, . . . , an of n ≤ 100000 integers on one line, denoting the profit/loss
for connecting each house on a street of length n. The entry at position i, 1 ≤ i ≤ n, is positive for
profit and negative for loss. We have many streets of data to process and a single line containing only
one integer denotes the end of input (this scenario is not processed). We can assume each scenario has
at least one positive house value ai
, since otherwise Circus would not even consider cabling that street.
The output of your program, one line per each scenario, is the maximum profit obtainable for that
street.
Sample Input:
10 -4 5
3 -4 5
3 -10 4 41 -1
10 0 20 -4 -3 8 -7 4
4 4 -3 1 0 0 -4 1 3 -4 7 -2 -2 3
1
Sample Output
11
5
45
31
9
1
Submission 1: fibreBrute.ext
There is a natural simple brute-force algorithm that tries and sums every subsequence ai + ai+1 +
ai+2 + · · · + aj−1 + aj for 1 ≤ i ≤ j ≤ n. Then return the maximum of all combinations of starting
positions i and ending positions j This algorithm has running time O(n
3
). With a simple observation
that, one can compute both the sums ai + · · · + aj+1 and ai+1 + · · · + aj from ai + · · · + aj with one
addition/subtraction, we can get a O(n
2
) algorithm. An implementation of this algorithm is required
for a program named fibreBrute.ext, where ext is an extension of the programming language of your
choice.
Submission 2: fibreDC.ext
For this part of the assignment we want to develop an even higher performance algorithm based on the
divide-and-conquer design approach. An O(n lg n) algorithm is possible by using an algorithm similar
to the ‘counting inversions’ algorithm given in lectures. Consider the following sequence:
a1, a2, . . . , a n
2 −1, an/2, a n
2 +1, . . . , an−1, an
An optimal solution either uses the element an/2 or not. So we can take the maximum of three cases:
recursively solve subproblem a1, . . . , a n
2 −1, recursively solve subproblem a n
2 +1, . . . , an, or the “conquer”
case that includes an/2. Submit a program named fibreDC.ext.
Submission 3: fibreDP.ext
Finally we want to improve to an O(n) time algorithm. You should use dynamic programming to solve
this case. Submit a problem named fibreDP.ext.
Comments
The markers will quickly look at the last of each of your submissions to make sure that you implement
all three algorithms and not just submit the fastest one, say fibreDP.ext, to the automarker for all
problems. The first implementation fibreBrute.ext is worth one mark and the other two improvements
are worth two marks each. There will be easy and hard test cases loaded on the automarker for the
two problems worth two marks. The number of submissions per problem is limited to 8 before a 20%
deduction is applied (assuming you solve a particular problem eventually). Note that for the hard test
cases the sums may require arbitrary precision integers (e.g. use Python 3 ints, Java BigInteger data
type, or C/C++ GMP library).
2