csc118 topic 2
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CSC118 – FUNDAMENTALS OF ALGORITHM DEVELOPMENT Chapter 2: Introduction to Problem Solving Using Computer A. Problem Solving 1. What is problem? • Unsettled matter demanding solutions or decision and requiring usually considerable thought or skill for its proper solution or decision 2. What is solution? • An action or process of solving a problem, also; • The fact or state of a problem being solved, also; • An answer to or means of answering a problem. • From the definition, the problem and solution are interrelated and therefore we believe that a problem should not be investigated separately from its solution. Therefore, to solve a problem, three important steps should be performed: i. Understand the problem thoroughly ii. Understand the conditions and requirements of the problem iii. Search for alternative solutions and select a general solution 3. Are computers intelligence? • Computers are very powerful machines but like other machines posses no intelligence. They programmed to solve problems. 4. What is a program? • A program is a set of instructions which are commands to computers to perform specific operations on data. Instructions within a program are organized in such a way, when the program is run on a computer; it results in the solution of a problem. 5. What is a programmer? • People who write programs for computers are called programmers. It is the programmer’s responsibility to write a correct program since a computer only faithfully obeys the commands specified by the instructions; it does not correct them if they are in error. If the program is not correct, erroneous results are obtained.
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1 class hour, 2 laboratory hours - 7 weeks; 1 creditThe latest version of a widely used spreadsheet program will be taught. Topics will include creating and problem-solving using spreadsheets, entering data and formulas, correcting errors, the range, copy and formatting instructions, printing, tables, and graphs. Not open to students who have successfully completed CSC
Transcript of csc118 topic 2
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputerA. ProblemSolving
1. Whatisproblem?
Unsettled matter demanding solutions or decision and requiring usually considerablethoughtorskillforitspropersolutionordecision
2. Whatissolution?
Anactionorprocessofsolvingaproblem,also; Thefactorstateofaproblembeingsolved,also; Ananswertoormeansofansweringaproblem.
From the definition, the problem and solution are interrelated and thereforewe believe that aproblem should not be investigated separately from its solution. Therefore, to solve a problem,
threeimportantstepsshouldbeperformed:
i. Understandtheproblemthoroughly
ii. Understandtheconditionsandrequirementsoftheproblem
iii. Searchforalternativesolutionsandselectageneralsolution
3. Arecomputersintelligence?
Computersareverypowerfulmachinesbutlikeothermachinespossesnointelligence.Theyprogrammedtosolveproblems.
4. Whatisaprogram?
Aprogram isa setof instructionswhichare commands to computers toperform specificoperationsondata. Instructionswithinaprogramareorganized in suchaway,when the
programisrunonacomputer;itresultsinthesolutionofaproblem.
5. Whatisaprogrammer?
Peoplewhowriteprogramsforcomputersarecalledprogrammers. It istheprogrammersresponsibility to write a correct program since a computer only faithfully obeys the
commandsspecifiedbytheinstructions;itdoesnotcorrectthemiftheyareinerror.Ifthe
programisnotcorrect,erroneousresultsareobtained.
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
Toproduce a correctprogram, aprogrammer goes through two (2)differentbut relatedphases:theproblemsolvingphaseandtheprogrammingphase.
a. Problemsolvingphase:
i. First, acquire a thorough understanding of the nature of the problem, and
deriveitsspecificationandrequirement.
ii. Next,determine andorganize theorderofoperation and computation to be
performedtosolvetheproblem.
Theoutputof theproblemsolvingphase is theproblem solution in someacceptablerepresentationalformsuchasadescription inhighlystructured
English(pseudocode)oraflowchart.Thisistheonewhatwecalledsolution
algorithmorforshort,analgorithm.
b. Programmingphase(Implementationphase):
i. Write the instructions for performing the predetermined operation and
computationsusingsuitableprogramminglanguage.
The result is a computer program, which is run on a computer and anyerrorsdiscoveredarecorrected.
A correct program is thus obtained and is ready to be used wheneverrequired.
B. WhatisAlgorithm?
Thereisnogeneraldefinitionofalgorithmaccepted. Butwecansaythatalgorithmis:
i. Astepbystepproblemsolvingprocedure
ii. Asequenceofinstructionthattellhowtosolveaparticularproblem.
iii. Asetofinstructionforsolvingaproblem,especiallyonacomputer.
iv. Acomputablesetofstepstoachieveadesiredresult.
However,mostagreethatalgorithmhassomethingtodowithdefininggeneralizedprocessestogetoutputfromtheinput.
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
Therefore,wecanconcludethat:o Algorithm a stepbystepproblem solvingprocess inwhicha solution isarrived ina
finiteamountoftime,OR
o Analgorithmisafinitelistofsequentialstepsspecifyingactionsthatifperformedresultinsolutionofaspecificproblem.
C. HistoryofAlgorithm
ThewordAlgorithmcomesfromthenameoffamousPersianmathematician,AbuJafarMohammedIbnMusaAlKhowarizmi(A.D.825).Heisknownforhisextensiveworkinalgebra.
D. RequirementofAlgorithm
Thealgorithmshouldbehasthefollowingrequirement:i. Finiteness
ii. Definiteness
iii. Effectiveness
iv. Input
v. Output
1. Finiteness
Analgorithmmusteventuallyhalt(endup)afteritsstepshavebeenperformedafinitenumberoftimes.
Analgorithmthatisnotguaranteedtohaltcannotbeimplementedbyeitherhumansormachines.
Example:Whathappenedifwearenonstoppourwaterinaglass?
2. Definiteness
Everyactionspecifiedatanystepofanalgorithmmustbepreciselydefined. Everyactioncontainedinanalgorithmmustbeclearandnotsubjecttodifferent
interpretations.Inotherwords,eachactiondescribedmustbeunambiguous.
Forexample:GivengrammarEE+E|E*E.WhathappenifwederivesententialformE+E*EfromproductionE?
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
3. Effectiveness
Everysteporactionspecifiedinanalgorithmmustbeexecutable. Example:
a. CanweconverttemperaturefromFahrenheittoCelsius?
b. CanweconvertcurrencyfromUSDtoRM?
c. Canwesort100numbersinascendingorder?
4. Input
Analgorithmmayreceiveinputsfromoutside. Example:Calculatetheareaofonecircle.Whatistheinput?
5. Output
Analgorithmmustproduceoneormoreoutput. Example:Calculatetheareaofonecircle.Whatistheoutput?
E. AlgorithmandLogicalThinking
Todevelopthealgorithm,theprogrammerneedstoask:1. Whatdatahastobefedintothecomputer?
2. WhatinformationdoIwanttogetoutofthecomputer?
3. Logic:Planningtheprocessingoftheprogram.Itcontainstheinstructionsthatcausethe
inputdatatobeturnedintothedesiredoutputdata.
F. SearchingAlgorithm
Searchingalistforagivenitemisoneofthemostcommonoperationsperformedonlistorarray.
Tosearchthelist,weneedthepiecesofinformationwhichare:1. Thelist.
Forexample:a. Abookcontainingapagesnumbers.
b. Arraycontainingalistofelements.
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
2. Thelengthoflist.
Forexample:a. Bookhasthenumberofpagesfrom1toN.
b. Arrayconsistoffinitenumberofelements,i.eE=[1,2,3,,N].
3. Theitemforwhichwearesearchingfor.
Forexample:a. Wewanttosearchpagenumber4inabook.
b. Searchnumber3fromelementofarray,E=[1,2,3,N].
Afterthesearchiscompleted:4. IftheitemisfoundreportSuccessandreportthelocationwheretheitemisfound.
5. Iftheitemisnotfound,thereportfailure.
Therefore,toaccommodate4and5,wewillwriteafunctionorprocedurethatreturnavalue. Ifthesearchitemisfoundinthelist,thefunctionorprocedurereturnsthelocationin
thelistwherethesearchitemisfound.
Otherwise,itreturn1,indicatingthatthesearchingisunsuccessful.
Fromthisoutput(locationoftheitembeingsearch,and1),itisclearthatthevaluereturningfunction(procedure),hasthree(3)parameters.
1. Thearraythatcontainingthelist,letwewriteaslist.
2. Thelengthofthelist,letwewriteaslistLength.(notethatthelistLength
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputerG. ProblemSolvingusingDifferentAlgorithm(LinearSearchAlgorithmandBinarySearchAlgorithm)
Forinstance,wesearchspecificpageinabookusingmethod:1. Linearsearchoralsoknownsequentialsearchalgorithm.
2. Binarysearchalgorithmoralsoknownchopalgorithm.
Weknowthatpagenumberinabookisinsequence.Howisthealgorithmtofindtheparticularpageinabook?
Whatinformationdoweneed? Listofpageofabook,List. Numbersofpageofabook,listLength.(listLength
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
Pseudocode:
Problem:Searchpage(list[],listLength,searchItem)found=FALSElist[]={1,2,3,4,5,6,7,8,9,10}listLength=10searchItem=4loc01.Start2.DOWHILEloc
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputerI. BinarySearch
Abinarysearchusesthedivideandconquertechniquetosearchthelist.1. First,searchItemiscomparedwiththemiddleelementofthelist.
a. IFthesearchItemislessthanthemiddleelementofthelist,werestrictthe
searchtothelowerhalfofthelist.
b. ELSE,wesearchtheupperhalfofthelist
Whatinformationdoweneed?1. Listofpageofabook,List.
2. Numbersofpageofabook,listLength.(listLength
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputer
PseudocodeProblem:Searchpage(list[],listLength,searchItem)found=FALSElist[]={1,2,3,4,5,6,7,8,9,10}listLength=10searchItem=4first=0last=listLength11.Start2.DOWHILEfirstsearchItem last=middle1 ELSE first=middle+1 ENDIFENDDO3.IFfoundisTRUE returnandreportthemiddleELSEreturn1ENDIF4.Stop
IterationofbinarysearchIteration first last middle list[middle] Found
1 0 9 4 5 FALSE2 0 3 1 2 FALSE3 2 3 2 3 FALSE4 3 3 3 4 TRUE
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CSC118FUNDAMENTALSOFALGORITHMDEVELOPMENTChapter2:IntroductiontoProblemSolvingUsingComputerJ. BubbleSort
PseudocodeBubbleSort(list[],listLength)iteration1index01.Start2.DOWHILEiteration
