IntroductiontoBasicDataStructuresandAlgorithmsIntroductiontoBasicDataStructuresandAlgorithmsClassificationofDataStructures

ArraysLinkedListStackQueueTreeHeapDictionaryHashTableGraph

ReferencesIntroductiontoBasicDataStructuresandAlgorithmsBeforeintroducingdatastructuresweshouldunderstandthatcomputersdostore,retrieve,andprocessalargeamountofdata.Ifthedataisstoredinwellorganizedwayonstoragemediaandincomputer'smemorythenitcanbeaccessedquicklyforprocessingthatfurtherreducesthelatencyandtheuserisprovidedfastresponse.

Datastructureintroductionreferstoaschemefororganizingdata,orinotherwordsadatastructureisanarrangementofdataincomputer'smemoryinsuchawaythatitcouldmakethedataquicklyavailabletotheprocessorforrequiredcalculations.Adatastructureshouldbeseenasalogicalconceptthatmustaddresstwofundamentalconcerns.First,howthedatawillbestored,andsecond,whatoperationswillbeperformedonit?Asdatastructureisaschemefordataorganizationsothefunctionaldefinitionofadatastructureshouldbeindependentofitsimplementation.ThefunctionaldefinitionofadatastructureisknownasADT(AbstractDataType)whichisindependentofimplementation.Theimplementationpartisleftondeveloperswhodecidewhichtechnologybettersuitstotheirprojectneeds.

Forexample,astackADTisastructurewhichsupportsoperationssuchaspushandpop.Astackcanbeimplementedinanumberofways,forexampleusinganarrayorusingalinkedlist.

Alongwithdatastructuresintroduction,inreallife,problemsolvingisdonewithhelpofdatastructuresandalgorithms.Analgorithmisastepbystepprocesstosolveaproblem.Inprogramming,algorithmsareimplementedinformofmethodsorfunctionsorroutines.Togetaproblemsolvedwenotonlywantalgorithmbutalsoanefficientalgorithm.Onecriteriaofefficiencyistimetakenbythealgorithm,anothercouldbethememoryittakesatruntime.

Sometimes,wecanhavemorethanonealgorithmforthesameproblemtoprocessadatastructure,andwehavetochoosethebestoneamongavailablealgorithms.Thisisdonebyalgorithmanalysis.Thebestalgorithmistheonewhichhasafinebalancebetweentimetakenandmemoryconsumption.But,asweknowthebestexistsrarely,andwegenerallygivemoreprioritytothetimetakenbythealgorithmratherthanthememoryitconsumes.Also,asmemoryisgettingcheaperandcomputershavemorememorytodaythanprevioustime,therefore,runtimeanalysisbecomesmoresignificantthanmemory.Theanalysisofalgorithmsisanentirelyseparatetopicandwewilldiscussthatseparately.

ClassificationDataStructuresDatastructurescanbebroadlyclassifiedintwocategorieslinearstructuresandhierarchicalstructures.Arrays,linkedlists,stacks,andqueuesarelinearstructures,whiletrees,graphs,heapsetc.arehierarchicalstructures.

Everydatastructurehasitsownstrengths,andweaknesses.Also,everydatastructurespeciallysuitstospecificproblemtypesdependingupontheoperationsperformedandthedataorganization.Forexample,anarrayissuitableforreadoperations.Followingisaquickintroductiontoimportantdatastructures.

ArraysArraysarestaticallyimplementeddatastructuresbysomeprogramminglanguageslikeCandC++hencethesizeofthisdatastructuremustbeknownatcompiletimeandcannotbealteredatruntime.Butmodernprogramminglanguages,forexample,Javaimplementsarraysasobjectsandgivetheprogrammerawaytoalterthesizeofthematruntime.Arraysarethemostcommondatastructureusedtostoredata.

Arraysareunarguablyeasierdatastructurestouseandaccess.Butinsertinganitemtoanarrayanddeletingitfromthearrayaresituationdependent.Ifyouwanttoinsertanitemataparticularpositionwhichisalreadyoccupiedbysomeelementthenyouhavetoshiftallitemsonepositionrightfromthepositionnewelementhastobeinsertedtheninsertthenewitem.Thetimetakenbyinsertoperationisdependonhowbigthearrayis,andatwhichpositiontheitemisbeinginserted.Thesameistrueaboutdeletionofanitem.

IfthearrayisunsortedthensearchoperationisalsoprovedcostlyandtakesO(N)timeinworstcase,whereNissizeofthearray.ButifthearrayissortedthensearchperformanceisimprovedmagicallyandtakesO(logN)timeinworstcase.

LinkedListLinkedlistdatastructureprovidesbettermemorymanagementthanarrays.Becauselinkedlistisallocatedmemoryatruntime,so,thereisnowasteofmemory.Performancewiselinkedlistisslowerthanarraybecausethereisnodirectaccesstolinkedlistelements.

Linkedlistisprovedtobeausefuldatastructurewhenthenumberofelementstobestored

KishoreHighlightand linear

isnotknownaheadoftime.

Therearemanyflavorsoflinkedlistyouwillsee:linear,circular,doubly,anddoublycircular.

StackStackisalastinfirstoutstrategydatastructurethismeansthattheelementstoredinlastwillberemovedfirst.Stackhasspecificbutveryusefulapplicationssomeofthemareasfollows:

SolvingRecursionrecursivecallsareplacedontoastack,andremovedfromthereoncetheyareprocessed.EvaluatingpostfixexpressionsSolvingTowersofHanoiBacktrackingDepthfirstsearchConvertingadecimalnumberintoabinarynumber

QueueQueueisafirstinfirstoutdatastructure.Theelementthatisaddedtothequeuedatastructurefirst,willberemovedfromthequeuefirst.Dequeue,priorityqueue,andcircularqueuearethevariantsofqueuedatastructure.Queuehasthefollowingapplicationuses:

Accesstosharedresources(e.g.,printer)MultiprogrammingMessagequeue

TreesTreeisahierarchicaldatastructure.Theverytopelementofatreeiscalledtherootofthetree.Excepttherootelementeveryelementinatreehasaparentelement,andzeroormorechildrenelements.Allelementsintheleftsubtreecomebeforetherootinsortingorder,andallthoseintherightsubtreecomeaftertheroot.

Treeisthemostusefuldatastructurewhenyouhavehierarchicalinformationtostore.Forexample,directorystructureofafilesystemtherearemanyvariantsoftreeyouwillcomeacross.SomeofthemareRedblacktree,threadedbinarytree,AVLtree,etc.

HeapHeapisabinarytreethatstoresacollectionofkeysbysatisfyingheapproperty.Maxheapandminheaparetwoflavorsofheapdatastructure.Theheappropertyformaxheapis:eachnodeshouldbegreaterthanorequaltoeachofitschildren.While,forminheapitis:eachnodeshouldbesmallerthanorequaltoeachofitschildren.Heapdatastructureisusuallyusedtoimplementpriorityqueues.

DictionaryDictionaryisadatastructurethatmaintainsasetofitemsindexedonbasisofkeys.

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Dictionarystoresdatainformofkeyelementpairs.

HashTableHashTableisagainadatastructurethatstoresdatainformofkeyelementpairs.Akeyisanonnullvaluewhichismappedtoanelement.And,theelementisaccessedonthebasisofthekeyassociatedwithit.Hashtableisausefuldatastructureforimplementingdictionary.

GraphGraphisanetworkeddatastructurethatconnectsacollectionofnodescalledvertices,byconnections,callededges.Anedgecanbeseenasapathorcommunicationlinkbetweentwonodes.Theseedgescanbeeitherdirectedorundirected.Ifapathisdirectedthenyoucanmoveinonedirectiononly,whileinanundirectedpaththemovementispossibleinbothdirections.

LastWordInthistutorialwesawabriefintroductionofvariousimportantdatastructures.Wealsotalkedofwhatdatastructuresare,andwhydatastructuressomuchimportantforinformationsystems.Datastructuresalongwithalgorithmsisacoresubjectofcomputerscience.Hopeyouhaveenjoyedreadingthistutorial.Pleasedowriteusifyouhaveanysuggestion/commentorcomeacrossanyerroronthispage.Thanksforreading!

References1. AlgorithmDesign[Foundations,Analysis,andInternetExamples]2. Algorithms,4thEdition3. HandbookofDataStructuresandApplications

copyright 2015 cs-Fundamentals.com [By Krishan Kumar]