2018 Algorithmics Written examination · A correct answer scores 1; an incorrect answer scores 0....

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ALGORITHMICS (HESS) Written examination Tuesday 20 November 2018 Reading time: 3.00 pm to 3.15 pm (15 minutes) Writing time: 3.15 pm to 5.15 pm (2 hours) QUESTION AND ANSWER BOOK Structure of book Section Number of questions Number of questions to be answered Number of marks A 20 20 20 B 18 18 80 Total 100 Students are permitted to bring into the examination room: pens, pencils, highlighters, erasers, sharpeners, rulers and one scientific calculator. Students are NOT permitted to bring into the examination room: blank sheets of paper and/or correction fluid/tape. Materials supplied Question and answer book of 23 pages Answer sheet for multiple-choice questions Instructions Write your student number in the space provided above on this page. Check that your name and student number as printed on your answer sheet for multiple-choice questions are correct, and sign your name in the space provided to verify this. All written responses must be in English. At the end of the examination Place the answer sheet for multiple-choice questions inside the front cover of this book. Students are NOT permitted to bring mobile phones and/or any other unauthorised electronic devices into the examination room. © VICTORIAN CURRICULUM AND ASSESSMENT AUTHORITY 2018 SUPERVISOR TO ATTACH PROCESSING LABEL HERE Victorian Certificate of Education 2018 STUDENT NUMBER Letter

Transcript of 2018 Algorithmics Written examination · A correct answer scores 1; an incorrect answer scores 0....

Page 1: 2018 Algorithmics Written examination · A correct answer scores 1; an incorrect answer scores 0. Marks will not be deducted for incorrect answers. No marks will be given if more

ALGORITHMICS (HESS)Written examination

Tuesday 20 November 2018 Reading time: 3.00 pm to 3.15 pm (15 minutes) Writing time: 3.15 pm to 5.15 pm (2 hours)

QUESTION AND ANSWER BOOK

Structure of bookSection Number of

questionsNumber of questions

to be answeredNumber of

marks

A 20 20 20B 18 18 80

Total 100

• Studentsarepermittedtobringintotheexaminationroom:pens,pencils,highlighters,erasers,sharpeners,rulersandonescientificcalculator.

• StudentsareNOTpermittedtobringintotheexaminationroom:blanksheetsofpaperand/orcorrectionfluid/tape.

Materials supplied• Questionandanswerbookof23pages• Answersheetformultiple-choicequestions

Instructions• Writeyourstudent numberinthespaceprovidedaboveonthispage.• Checkthatyournameandstudent numberasprintedonyouranswersheetformultiple-choice

questionsarecorrect,andsignyournameinthespaceprovidedtoverifythis.• AllwrittenresponsesmustbeinEnglish.

At the end of the examination• Placetheanswersheetformultiple-choicequestionsinsidethefrontcoverofthisbook.

Students are NOT permitted to bring mobile phones and/or any other unauthorised electronic devices into the examination room.

©VICTORIANCURRICULUMANDASSESSMENTAUTHORITY2018

SUPERVISOR TO ATTACH PROCESSING LABEL HEREVictorian Certificate of Education 2018

STUDENT NUMBER

Letter

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2018ALGORITHMICSEXAM 2

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Question 1Whichmethodormethodscanbeusedtocheckforthecorrectnessofalgorithms?A. inductiononlyB. contradictiononlyC. inductionandcontradictionD. oncewritten,analgorithmisalreadyknowntobecorrect

Question 2ArequirementofCobham’sthesisisthatitA. assumesallPproblemsareeasyandallNPproblemsarehard.B. onlyconsidersalgorithmsthataredeterminedtobepracticallyfeasible.C. considersthesizeoftheinputtobethemostimportantcomponentforsolvability.D. considersconstantfactorsandlower-ordertermsasimportantcomponentsforsolvability.

Question 3Amanagerisattemptingtocoordinateseveralimpatientcustomerswaitinginline.Tobefairesttothecustomers,whichabstractdatatype(ADT)shouldthemanagernot use?A. decisiontreeB. directedlistC. queueD. stack

SECTION A – Multiple-choice questions

Instructions for Section AAnswerallquestionsinpencilontheanswersheetprovidedformultiple-choicequestions.Choosetheresponsethatiscorrectorthatbest answersthequestion.Acorrectanswerscores1;anincorrectanswerscores0.Markswillnotbedeductedforincorrectanswers.Nomarkswillbegivenifmorethanoneansweriscompletedforanyquestion.UsetheMasterTheoremtosolverecurrencerelationsoftheformshownbelow.

T naT n

bkn

d

n

n

c( ) =

+

>

=

if

if

1

1 wherea>0,b>1,c≥0,d≥0,k > 0

anditssolutionT nO nO n nO n

a ca c

c

cb

bba

( )( )( log )( )

loglogloglog

=

<=

ififif bb a c>

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Question 4Considerthefollowinggraph.

Whichofthefollowingpropertiesdoesthisgraphhave?A. directedandacyclicB. cyclicandweightedC. cyclicandfullyconnectedD. non-directedandnon-connected

Question 5WhichoneofthefollowingmustexistinthedefinitionofanADT?A. auniqueidentifierB. asetofoperationsC. aconcreterepresentationofdataD. theimplementationofoperations

Question 6WhichoneofthefollowingbeststatesthedifferencebetweenalistADTandadictionaryADT?A. Findingtheminimumiteminasortedlistisusuallyfasterthanfindingtheminimumitemina

dictionary.B. Findingthemaximumiteminadictionaryisusuallyfasterthanfindingthemaximumiteminasorted

list.C. Alistcanhaveitsvaluesaccessedviaanintegerindex,whileadictionarycannot.D. PrioritiesaredefinedwithinalistADT,whileadictionaryhasnoprioritiesintheADT.

Question 7Whentestingtofindoutwhetheragraphhasmultipleconnectedcomponents,whichoneofthefollowingmodificationstoabasicimplementationofPrim’salgorithmisthemostappropriate?A. Choosethemaximumweightededgetoconnectanodetothegrowingtree.B. RunPrim’salgorithmoneverynodeandkeeptrackofuniquesetsofnodes.C. Deleteallexistingedgesoftheexistinggraphandcreatenewedgestoconnecteachnode.D. NomodificationsneedtotakeplaceasPrim’salgorithmcanalreadytestformultipledisconnected

components.

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Question 8ForwhichoneofthefollowinggraphswouldtheFloyd-Warshallalgorithmreturnall-pairshortestpaths?

A

CB

–2–1

–3

A

CB

2–4

1

A B

C D

–2

2

3 –2

A. B.

C. D.A B

C D

–2

2

–1 –41 1

Question 9Assumequicksortalwayschoosestherightmostelementasapivotwhencreatingpartitions.Thesortingmaintainstherelativeorderofelementswhilepartitioningandstopstherecursionattheemptyarray.Giventhearray{1,2,3,4,5,6,7,8},howmanypivotswillbechosenbeforethealgorithmreturnsasortedarray?A. 0B. 1C. 3D. 8

Question 10Considerthefollowingpseudocodeforthealgorithmunknown(x),wherexisanodeofagraph.

Algorithm unknown(x) Let x.discovered = True

For eachNode in x.adjacentNodes

If eachNode.discovered is not True Then

unknown(eachNode)

EndIf

EndFor

Whichalgorithmdoesthepseudocodebestrepresent?A. best-firstsearchB. depth-firstsearchC. bruteforcesearchD. breadth-firstsearch

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Question 11

cloud

10010 1

1

1100

10

WhichoneofthefollowingADTswouldbebestsuitedtomodelthenetworktopologydiagramshownabove?A. aweighted,directedgraphB. astackwithkeysC. adirectedgraphD. anarray

Use the following information to answer Questions 12 and 13.Considerthefollowingthreealgorithms,whichalloperateoninputsofsizenelements,andtheirBig-OorBig-Θresourcerequirements:• AlgorithmA:O(n)worstcasetime• AlgorithmB:Θ(2n)bestcasetime• AlgorithmC:Θ(nlogn + n)bestcasetimeandworstcasetime

Question 12WhichoneofthefollowingstatementsaboutalgorithmsA,BandCiscorrect?A. AlgorithmsAandBareincomplexityclassP.B. AlgorithmsBandCareincomplexityclassP.C. AlgorithmsAandCareincomplexityclassP.D. AlgorithmsAandCarenotincomplexityclassP.

Question 13WhichoneofthefollowingstatementsaboutalgorithmsA,BandCiscorrect?A. NoalgorithmwillterminateinO(1)timeonanylargeninputs.B. AlgorithmAcouldterminateinO(1)timeonsomelargeninputs.C. AlgorithmBcouldterminateinO(1)timeonsomelargeninputs.D. AlgorithmCcouldterminateinO(1)timeonsomelargeninputs.

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Question 14SameerarunsanalgorithmonthegraphbelowtocomputeapathfromAtoB.Thealgorithmbecomestrappedinacycle.

B C

A

WhichoneofthefollowingalgorithmshasSameeraused?A. PageRankalgorithmB. Dijkstra’salgorithmC. breadth-firstsearchwithoutmarkingpreviousnodesD. depth-firstsearchwithoutmarkingpreviousnodes

Question 15CyclistSergeihasacleverplantowineveryracethatheenters.Hewillstartatthefrontoftheracepedallingslowlyat5km/h.Everytimesomeonecatchesuptohim,Sergeiwilldoublehisspeed.Assumingthatthemaximumspeedforanycyclistis60km/h,howmanypeoplewillcatchSergeibeforehecannotgoanyfaster?A. 2B. 3C. 4D. 5

Question 16Analgorithmtakesasetofinputsandperformscalculationsonit.Theoutputfromthealgorithmconsistsofasetofnumbersandlettersthatarerelatedtotheinitialinputs.TheoutputfromthealgorithmcanbeverifiedinworstcaseO(n2)time.Giventhisinformation,itcanbesaidthatthealgorithmisA. decidableandincomplexityclassNP.B. undecidableandincomplexityclassNP.C. decidableandincomplexityclassPandnotincomplexityclassNP.D. undecidableandincomplexityclassPandnotincomplexityclassNP.

Question 17AneuralnetworkcanbeusedtoA. findexactsolutionstocomputationallyundecidableproblems.B. demonstratethatSearle’sChineseRoomArgumenthasmerit.C. processcomplexinputswithnoknownrelationships.D. alwayssolveproblemsfasterthanDNAcomputing.

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END OF SECTION ATURN OVER

Use the following information to answer Questions 18 and 19.ThefollowingisaproofbycontradictionthatPrim’salgorithmgeneratesaminimalspanningtree(MST),withsomedetailsomitted:• LetGbeagraphwithvertices,V,andaminimalspanningtree,T*.• LetTbeaspanningtreegeneratedbyPrim’salgorithmongraphG.• AssumeT≠T*.Lettheedge(u,v)beinTbutnotinT*.• When(u,v)wasaddedtoTbyPrim’salgorithm,itwastheminimumedgecrossingfromthesetof

vertices,S,thathadalreadybeenaddedtoT,tothesetofvertices,V – S,thathadnotbeenaddedtoT.• Let(x,y)beanedgeonthepathfromu to vinT*suchthatxisinSandyisinV – S.• Formanewtree,T**,byadding(u,v)toT*andremoving(x,y)fromT*.

Question 18Whichoneofthefollowingstatementsisnot correct?A. Theedge(u,v)existsbecauseT≠T*.B. Thereisapathfromu to vinT*becauseitisaspanningtree.C. T**isnotatreebecauseadding(u,v)toT*andremoving(x,y)fromT*createsacycle.D. T**isatreebecauseadding(u,v)toT*andremoving(x, y)fromT*doesnotcreateacycle.

Question 19Whichoneofthefollowingstatementsgeneratesthecontradictionneededtocompletetheproof?A. T**hasahigherweightthanT*,thusT*couldnotbetheMSTofG.B. T**hasalowerweightthanT*,thusT*couldnotbetheMSTofG.C. T**isnotatree,thusT*couldnotbetheMSTofG.D. T**isnotatree,thusT*istheMSTofG.

Question 20Simulatedannealinghasbeensuggestedasausefultechniquetocomputeaglobalminimumrainfalloveralargesetofrainfalldata.Whichheuristicappliedtosimulatedannealingismorelikelytoreturnaglobalminimumrainfall?A. increasetheprobabilityofchoosingaworsesolutionatrandomasrunningtimeincreasesB. decreasetheprobabilityofchoosingaworsesolutionatrandomasrunningtimeincreasesC. allowthesystemtemperaturetocoolquicklytofindasolutioninashortamountoftimeD. keepthesystemataconstanttemperaturetofindthebestsolutionwithinashortamountoftime

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2018ALGORITHMICSEXAM 8

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SECTION B – continued

Question 1 (2marks)DescribeonesimilarityandonedifferencebetweenaTuringmachineandamoderncomputer.

Question 2 (4marks)Eliseneedstouseapriorityqueueabstractdatatype(ADT).

WriteapriorityqueueADTspecificationforElise.

SECTION B

Instructions for Section BAnswerallquestionsinthespacesprovided.UsetheMasterTheoremtosolverecurrencerelationsoftheformshownbelow.

T naT n

bkn

d

n

n

c( ) =

+

>

=

if

if

1

1 wherea>0,b>1,c≥0,d≥0,k > 0

anditssolutionT nO nO n nO n

a ca c

c

cb

bba

( )( )( log )( )

loglogloglog

=

<=

ififif bb a c>

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SECTION B – continuedTURN OVER

Question 3 (4marks)Thefollowingalgorithmfindsthemaximumelementinalist.

Algorithm FIND_MAX(L): Input: L, a non-empty list of elements

If L has only one element

return first element of L as the maximum

EndIf

m = FIND_MAX(L without the first element)

If m is greater than the first element in L

return m

Else

return the first element of L

EndIf

a. Writearecurrencerelationanditssolutiontodescribetheworstcaserunningtimeofthealgorithmwhenthelistcontainsnelements. 3marks

b. WouldtheBig-Oforthebestcaserunningtimeofthealgorithmbesmallerthantheworstcaserunningtimeofthealgorithm?Justifyyouranswer. 1mark

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SECTION B – continued

Question 4 (2marks)Considerthefollowingrecurrencerelations.

S nS n n

O

n

n

T nT n O n

O

( )( )

( )( )

(

=

+

>

<

=

+

23

3

1

3

4

22

1

if

))

>

<

if n

n

1

2

a. WhatistheBig-OsolutiontoS(n)? 1mark

b. WhatistheBig-OsolutiontoT(n)? 1mark

Question 5 (3marks)Maryaminvestsincompaniesonthestockmarket.Sheiscurrentlyconsidering50potentialcompaniesshecaninvestinandhasestimatedthepotentialprofitsheislikelytoreceivefromeachcompanyoverthenext12months.TheinvestmentineachcompanyhasaninitialcostandMaryamhasafixedbudgetthatshecannotexceed.

DescribeadynamicprogrammingalgorithmthatMaryamcanusetoselectasetofcompaniestoinvestinthatwillprovidemaximumprofitforherbudget.

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SECTION B – continuedTURN OVER

Question 6 (5marks)Anewshoppingcentrehasbeenbuiltandhasattractedmanycustomers.Thecentre’smanagementhasnotedthatmanyofthesecustomersaregettinglostwithintheshoppingcentre.Thecentre’smanagementwantstodesignandbuildaninteractivemapapplicationthatwillallowcustomerstofindtheirwaytoeachshopfromfixedinformationkiosksaroundtheshoppingcentre.

a. NameandjustifyagraphADTthatwouldbestsuittheinteractivemapapplication. 3marks

b. Thecentre’smanagementhasdecidedtoinstallanadditionalinformationkiosk.

Explainhowtheadditionalinformationkioskcouldbeintegratedwithintheinteractivemapapplication.WhatchangestothegraphADTnamedinpart a.wouldhavetooccur? 2marks

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2018ALGORITHMICSEXAM 12

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SECTION B – continued

Question 7 (4marks)Considerthedecisiontreebelow.

weekday weekend

time > 9 amand time < 3 pm

time > 3 pmand time < 9 am

no homework homework

no homework homework

school sleep

sleep study

study

Representthisdecisiontreeusinglogicaloperationsinpseudocode.

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SECTION B – continuedTURN OVER

Question 8 (4marks)Proveviainductionthatthesumofthefirstnoddnumbersisthesameasn2,foralln≥1.

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SECTION B – Question 9–continued

Question 9 (9marks)Devicesthatarecapableofwirelesstransmissionarebecomingcheaperandeasiertointegrateintoexistingtechnology,suchasvacuumcleanersandrefrigerators.Thesedevicestypicallycommunicateusinganetwork.ThenetworkbelowshowsdevicesnamedA–O.

Grid 1 2 3 4 5 6 7 8 9

a

b

c

d

e

f

g

h

i

O

C

F

E

I

G

D

JH

KB

A

M

N

L

Thenetworkabovehasthefollowingconditions:• Eachdeviceisawareofitscoordinatesandthereisacompletelistofdevices.• Eachsquarerepresentsa50m×50marea.• Forsuccessfulconnectionoverwirelesstransmission,devicesmustbewithinrange:twosquares

verticallyorhorizontallyandonesquarediagonally.Forexample,deviceAcancommunicatewiththosesquareswithanunderscore.

• Eachdevicecanrelaydatabetweennodeswithinrange.Forexample,deviceAcancommunicatewithdeviceE,whichcanthencommunicatewithdeviceF.

• Eachdevicecanreturntemperaturevaluesmeasuredwithinitssquare.

a. Whichdevice(s)cannotsuccessfullyconnectoverwirelesstransmissionwithanyotherdevice? 1mark

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SECTION B – continuedTURN OVER

b. DescribehowtheFloyd-Warshallalgorithmcanbeusedtocheckifalldevicescancommunicatewithanyotherdevice. 2marks

c. Writeanalgorithmtocomputetheaveragetemperatureofalldevicesinthenetwork,givenalltemperaturesinaninputlist,temperature_list.Somedevicesmaybedefectiveandreturn–255astheirtemperaturevalue.Thealgorithmshouldnotincludethesetemperaturesinthecalculation. 6marks

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2018ALGORITHMICSEXAM 16

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SECTION B – continued

Question 10 (4marks)Joedeliversgroceriestothesamefivehouseseverydayaspartofhisdeliverybusiness.Toconservefuel,hecomputedthelengthofallpossibleroutesbetweenhishomeandthosefivehousestofindtheminimumroute.

a. HowmanyroutesdidJoecompute? 1mark

b. Joe’salgorithmtodeterminetheminimumrouteisanexampleofwhatalgorithmicdesignpattern? 1mark

c. AsJoe’sdeliverybusinessgrowsandmorehousesareaddedtothedeliverylist,willJoe’salgorithmicapproachstillbeusefulforcomputingtheoptimaldeliveryroute?Justifyyouranswer. 2marks

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SECTION B – continuedTURN OVER

Question 11 (4marks)Considerthefollowingalgorithmforsortingalistofintegersinascendingorder,whichmakes useofanotheralgorithmcalledSORT2.AssumethatSORT2runsinΘ(n logn)timeonalistoflengthn,unlessthelistissortedindescendingorder,inwhichcaseSORT2runsinΘ(n2)time.

Algorithm SORT(L) INPUT: L, a list of integers

Let sorted = True

For each element x except the last in L

If x is greater than its right neighbour in L

Let sorted = False

EndFor

If sorted is False Then

Return the result of SORT2(L)

Else

Return L

EndIf

a. WhatisthebestcaserunningtimeofSORT?Writedownalistof10integersthatgivesthebestcaserunningtime. 2marks

b. WhatistheworstcaserunningtimeofSORT?Writedownalistof10integersthatgivestheworstcaserunningtime. 2marks

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2018ALGORITHMICSEXAM 18

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SECTION B – continued

Question 12 (2marks)

–5

–2 1

–2

2

1 0

A B

C D

E F

ExplainwhythegraphaboveisnotasuitableinputtoanaiveimplementationoftheBellman-Fordalgorithm.

Question 13 (3marks)DescribeDNAcomputingandexplainhowitcanbeusedasanalternativemethodofcomputation.Provideanexampleaspartofyourexplanation.

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SECTION B – continuedTURN OVER

Question 14 (9marks)Thestrategyusedforclimbingarockwallisveryimportant.Foragivenrockwall,thereisasetofnumberedhandholdsandfootholdsthatcanbechoseninsequencetoallowtheclimbertogettothetopofthewall.Longrouteswithhandholdsandfootholdsthatarespacedfarapartcancausetheclimbertotirequicklyandincreasetheirriskoffalling.Shortrouteswithcloselyspacedhandholdsandfootholdsallowclimberstopreserveenergyandmakeittothetop.YouhavebeenselectedasthestrategycoachoftheAustralianteamfortheClimbingWorldChampionships.Inparticular,youhavetoplotacourseforeachclimberoneachwall.

a. Whatinformationwouldyouneedabouteachwallandeachclimber?WhatADTwouldbebesttousetomodelthisproblem?Why? 3marks

b. WhatalgorithmwouldyouusetodeterminetheoptimalclimbingrouteusingtheADTfrompart a.?Inyouranswer,describehowyouwouldtranslatetheoutputfromyouralgorithmintomeaningfulinformationthattheclimbercoulduse.Alsoincludeanestimationofthetimecomplexityofyourapproachandhowitcomparestoabruteforceapproachtotheproblem. 6marks

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2018ALGORITHMICSEXAM 20

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SECTION B – continued

Question 15 (3marks)Socialmediaprofileshavebeenreceivedbyacompanythatplanstousethedatatoinferwhichusersitshouldtargetfirstinordertoinfluencelargecommunities.Thedatacontainsuserprofiles,theirlistsoffriendsandtheirpubliccomments.

Describeanalgorithmthatcouldbeusedtoidentifythemostinfluentialprofilesinthedata.

Question 16 (4marks)Bernieisdevelopingamobilerobotforanationalpark.Therobotwilltravelthroughtheparkusingexistingpathsanddepositanimalfoodatfeedingstations.Thesefeedingstationswillbechangedeveryseasontomatchthemovementofanimalsduringtheyear.Bernieiscurrentlydesigningthealgorithmthattherobotwillusetoselectthemostefficientpathitshouldtaketovisitallofthefeedingstationswhileminimisingthedistanceittravels.

WhatisthebestalgorithmforBernietousetodecidetheorderinwhichtherobotwillvisiteachfeedingstation?Willitguaranteeanoptimalsolution?Explainwhyorwhynot.

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SECTION B – continuedTURN OVER

Question 17 (4marks)Afarmersharesafieldwithanotherfarmer.Everyyeareachfarmercansell10cowsandreducetheirincomeby10%orbuy10cowsandincreasetheirincomeby10%ordonothing.Atthebeginningofeachyear,theavailableresourcesinthefield,asapercentage,changeby100minusthetotalnumberofcows.Forexample,assumethatthefieldhas100%resourcesand,atthebeginningoftheyear,Farmer1has50cowsandFarmer2has70cows,thustheresourceschangeto80%.Ifnextyearthetotalnumberofcowsis110,theresourceschangeto70%.Ifnextyearthenumberofcowsis90,theresourceschangeto80%.Iftheavailableresourcesatthebeginningofayeardropbelow50%,allcowsmustberemovedandbothfarmerslosetheirbusinesses.

Describeanalgorithmthatwillselectastrategythatmaximisesonefarmer’sincomeattheendoftwoyears,withoutlosingallofthisfarmer’scows.

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SECTION B – Question 18–continued

Question 18 (10marks)Twopirates,MontyandBlackbeard,havedecidedtodividetheirfortunes.MontymakesthefollowingpropositiontoBlackbeard:Choosebetweentakingthesquaremadeofgoldwhosesideisthehypotenuse(sidec)oftheright-angletriangleorthetwosquaresmadeofgoldwhosesidesareadjacenttotheright-angletriangle(sidesaandb),asshowninthediagrambelow.

c b

a

IfBlackbearddecidestotakethesquarewiththehypotenuse(sidec),hemustgiveacertainpercentageofthegoldtoMonty.

a. Writeanalgorithm,square_area,inpseudocodethatwillreturntheareaofanygoldensquare. 2marks

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23 2018ALGORITHMICSEXAM

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END OF QUESTION AND ANSWER BOOK

b. Assumesquare_areaexists.WriteanalgorithminpseudocodethatwilldeterminethebestdecisionforBlackbeardtomakeinordertomaximisetheamountofgoldhereceives.IfBlackbeardshouldchoosethesquarewiththehypotenuse(sidec)thenthealgorithmshouldreturnTrue,otherwiseitshouldreturnFalse. 4marks

c. WhatisthebestdecisionforBlackbeardtomaketomaximisetheamountofgoldhereceives?Justifyyouranswer. 2marks

d. Insteadofsquaresmadeofgold,MontyandBlackbeardmustsharecubesmadeofgold.

WhatisthebestdecisionforBlackbeardtomakeinthisinstance?Justifyyouranswer. 2marks