Hank Childs, University of OregonNovember 19, 2019

Lecture 15:Abstract Data Types

__. __ .__ __. __ ___ ___ ______ ___ .__ __. _______ _______ ___ .___________. ___| | | | | \ | | | | \ \ / / / | / \ | \ | | | \ | \ / \ | | / \| | | | | \| | | | \ V / | ,----' / ^ \ | \| | | .--. | | .--. | / ^ \ `---| |----` / ^ \| | | | | . ` | | | > < | | / /_\ \ | . ` | | | | | | | | | / /_\ \ | | / /_\ \| `--' | | |\ | | | / . \ __ | `----.__ / _____ \ | |\ | | '--' | | '--' | / _____ \ | | / _____ \\______/ |__| \__| |__| /__/ \__\ (_ ) \______(_ ) /__/ \__\ |__| \__| |_______/ |_______/ /__/ \__\ |__| /__/ \__\

_______.___________..______ __ __ ______ .___________. __ __ .______ _______ _______. / | || _ \ | | | | / || || | | | | _ \ | ____| / | | (----`---| |----`| |_) | | | | | | ,----'`---| |----`| | | | | |_) | | |__ | (----` \ \ | | | / | | | | | | | | | | | | | / | __| \ \

.----) | | | | |\ \----.| `--' | | `----. | | | `--' | | |\ \----.| |____.----) ||_______/ |__| | _| `._____| \______/ \______| |__| \______/ | _| `._____||_______|_______/

Logistics

• VisityourtestFridayNov22,1015am-1230pm• There_is_labthisweek• Nextweek:weirdweek– Labcanceled– NolectureThursNov28th (Thanksgiving)

• Only5lecturesleft(includingthisone)…wehavelotstodo.

Thisistheremainderoftoday’slecture

• Abstractdatatypes– Thinkaboutitfromtheperspectiveoftheuser– NOTtheimplementor

Datatypes

• Simpledatatypes– float,double,int,char,unsignedchar

• Complexdatatypes– Definedwithstructs

• Abstractdatatype– Accomplishedthroughfunctioncalls– Youdon’thavetoknowthedetails

Abstractdatatypes

• Twopieces:– Definebehavior(viafunctionprototypes)– Defineimplementation(viafunctions)

• Youcanhavemorethanoneimplementationforagivenbehavior

(Bad)Example:OneInterface,MultipleImplementations

Badexamplesincewearetalkingaboutdatatypes… thisisjustafunctionthatworksondata

BetterExample:Store/Fetch

• Abstractdatatypehastwomethods:– Store• Takesa“key”anda“value”

– Fetch• Takesa”key”,andreturnsa“value

• Example:– Key==UOID– Value==studentstruct

DETOUR

• Wearegoingtospendthenext15slides&30-40minutestalkingaboutanexample.

• ThisexamplewillthenbeusedtoshowADTs.• TheADTwilldostore/fetch• Weneedtwoideasforhowtodostore/fetch– Arrays– Hashtables

• Observation:• Idon’tneedtoknowanythingaboutADT

• Howisitimplemented?

• HowlongdoesStoretake?

• HowlongdoesFetchtake?

Initialize(&adt);

ToMotivateADT,WeNeedExamplesofDataStructuresThatCanDoStore/Fetch• TwoExamples:– Array– HashTable

OneDataStructureforStore/Fetch:Array• Observation:• Notverygeneric(int key,Studentvalue)

• WhynotpassinStoreFetchArray *insteadofvoid*?

• A:needthislater

voidArrayInitialize(StoreFetchArray *arr)

ComplexityforArray

• Store:O(1)• Fetch:O(N)

HashTable

• Idea:– Createabigarraywithkeysandvalues• (Justlikelastslide!)

– But:don’tinsertstartingfromthebeginning– Instead:insertinto“random”placesinthearray– Nottrulyrandom,asitneedstobereproducible– Typical:takekeyandperformsomemathoperationonit

Thiswillbeawhirlwindintrotohashtables.Wewillreturntothisidealater.

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 -1 -1 -1 -1 -1 -1

NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL

Tableindex

Key

Student

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 -1 -1 -1 -1 -1

NUL NUL NUL NUL xFF NUL NUL NUL NUL NUL

Tableindex

Key

Student

Store:UO_ID:951001234Student:“xFF”

Idea:TurnUO_IDintoanindex.

Inthiscase,%10.(muchmorecomplexideas)

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 -1 ..66 -1 -1 -1

NUL NUL NUL NUL xFF NUL xAF NUL NUL NUL

Tableindex

Key

Student

Store:UO_ID:951003266Student:“xAF”

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 ...44 ..66 -1 -1 -1

NUL NUL NUL NUL xFF xAA xAF NUL NUL NUL

Tableindex

Key

Student

Store:UO_ID:951012344Student:“xAA”

Idea:Slot4isfull… justusethe

nextslot(slot5).Keepgoinguntilyoufind

one,includingwraparounds

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 ...44 ..66 …45 -1 -1

NUL NUL NUL NUL xFF xAA xAF xB8 NUL NUL

Tableindex

Key

Student

Store:UO_ID:951012345Student:“xB8”

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 ...44 ..66 …45 -1 -1

NUL NUL NUL NUL xFF xAA xAF xB8 NUL NUL

Tableindex

Key

Student

Fetch:UO_ID:951045323

EASY:NULL

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 ...44 ..66 …45 -1 -1

NUL NUL NUL NUL xFF xAA xAF xB8 NUL NUL

Tableindex

Key

Student

Fetch:UO_ID:951012345

Morework… walkfromindex5to6to7… foundit!

HashTable

0 1 2 3 4 5 6 7 8 9

-1 -1 -1 -1 …34 ...44 ..66 …45 -1 -1

NUL NUL NUL NUL xFF xAA xAF xB8 NUL NUL

Tableindex

Key

Student

Fetch:UO_ID:951012355

Morework… walkfromindex5to6to7to8… not

there!

AnotherDataStructureforStore/Fetch:HashTable

• Observation:• Stillnotverygeneric.(int key,Studentvalue)

ComplexityforHashTable

• Store:itdepends– Thingsgowell:O(1)– Thingsgopoorly:O(n)

• Fetch:itdepends– Thingsgowell:O(1)– Thingsgopoorly:O(N)

• Getsintonewtopic… expectedperformance.

ToMotivateADT,WeNeedExamplesofDataStructuresThatCanDoStore/Fetch• TwoExamples:– Array– HashTable

DispatchTable

• Dispatchtable:allowsfor“methods”tobedefineonADT

• Donewithastructthatcontainspointerstofunctions

ADTstruct /dispatchtable&functioncalls

ConstructingADTfromStoreFetchArray orHashTable

ThisiswhyArrayStore/ArrayFetchneededtobevoid*

ADTinaction

Datastructureforspecificdatatype

(example:arrayofStudents)

Datastructurefor*any*datatype

(example:arrayof“void*”)

Abstractdatastructureforspecificdatatype

(example:searchforstudentnames)

Abstractdatastructurefor*any*datatype

(example:searchfor“void*”)

WhenDoIUseWhat?

Datastructureforspecificdatatype

(example:arrayofStudents)

Datastructurefor*any*datatype

(example:arrayof“void*”)

Abstractdatastructureforspecificdatatype

(example:searchforstudentnames)

Abstractdatastructurefor*any*datatype

(example:searchfor”void*”)

Whenwritingsomethingformyspecificprogram

WhenIhavedevelopedadatastructureIwantotherstouse

WhenIwanttosolveaproblemformany,manypeople

Never?(butalsowhatwejustdid)

Specificdatastructureforspecifictype

Specificdatastructureforgenerictype

Abstractdatatypes

Nomanagement/organization

ofdata

adt.c

• Fileadt.c isonline.Let’slookatitforawhile.

Project3A

• 3Aisalittlemismatched.• Iamreferringto“Fruit”asadispatchtable,butnotethatFruitisnotreallyanabstractdatatype.Itismorean“abstracttype.”

• Butthemachinery(dispatchtable)isthesame.

Project3A

Project3A

Stacks

Stacks• Adatastructure• 2methods:pushandpop• Sometimesathird:peek

Example:StackofIntegers

Stack:AsymptoticComplexity

• Push:O(1)• Pop:O(1)• Store:O(1)• Fetch:O(n)–àpopeachelementandlook,andthenrestore?