7 8 9 collections - york university...add(e e) on a set returns false if e is already in it (for a...

Collec&ons

EECS1022/Lespérance 1

EECS1012MOBILECOMPUTING

PROF.Y.LESPÉRANCEDept.ofElectricalEngineering&ComputerScience

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§  Problem:namingabunchofthingsCannotusevariables…willrunoutofnames!

§  Solu&onsTradi6onalapproach:name+index=arrayModernapproach:objectwithAPI=list,set,map

§  ComparisonArrayshavenoAPIandsufferfromfixedalloca6onThemoderncollec6onframeworkhasarichAPI

§  ButweoccasionallyusearraysForcompa6bilitywithlow-levelAPI(e.g.splitandargs)

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§  Representacollec&onofen&&esofthesametype

§  Declara&on:type[]name;e.g.int[]bag;

§  Instan&a&on:newtype[size],e.g.bag=newint[100];

§  Refertoelementsbyname[index],e.g.bag[0]=123;bag[1]=bag[0]+5;

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§  name.lengthrepresentsthearray’slength§  Indicesgofrom0tolength–1§ Mul&dimensionalarrayscanalsobeused

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Collec&ons


Ifwepickanintegerin[1,1M]randomly,howlikelyisittogetonewhosedigitsumisdivisibleby7?

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Computetheprobabilitybysampling10%ofthoseintegersandstorethesampleinacollec6on.

1.  UseArraysSeeSumDiv7_array.java

2.  UseCollec&onsSeeSumDiv7_coll.java

§  ListvsSetvsMapList:maycontainduplicatesandelementsareordered.Set:noduplicatesandnoorder.Map:key-valuepairs,keyunique.

§  TheInterfaces(akaAbstractDataTypes)List<E>,Set<E>,andMap<K,V>(usegenerics)

§  TheClasses(akaImplementa&ons)List:ArrayListandLinkedyList;Set:HashSetandTreeSetMap:HashMapandTreeMap

§  CommonAPIssize(),clear(),iterator(),toString()Methodstoinsert,delete,andsearchàCRUD

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Basic

size()

clear()

iterator()

Map

put(K,V),get(K),keySet()

containsKey(K)

containsValue(V)

List/Set

add(E)

remove(E)

contains(E)

ListOnly

add(int,E)

remove(int)

get(int)

OtherAPI

Theenhancedforloop

Collec&ons.sort(List)

Arrays…seeAPI

§  add(Ee)onasetreturnsfalseifeisalreadyinit(foralistalwaysreturnstrue)

§  remove(Ee)returnstrueiffeisfoundinthesetorlist;foralistremovesonlyfirstoccurrence

§  Collec&ons.sort(List<E>l)rearrangesltomakeitsorted(accordingtonaturalorder)

§  Arrays.asList(E[]a)returnsaListrepresenta&onofarraya

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Collec&ons


§  TraversingaList<E>bagi.e.goingthroughallofitselementsonebyone,isacommonopera&on:

for(Ee:bag){

System.out.println(e);

}

§  Similarlyforsets

§  Forlists,canalsodoanindexedtraversal:for(inti=0;i<bag.size();i++){

Ee=bag.get(i);System.out.println(e);

}

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Givenalist,determinewhetheritcontainsduplicateelements.

Canbedonein3ways:

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1.  Sortthelistandthentraverseittocheckforadjacentduplicates

2.  Createasetandthentrytoaddeachlistelementtoitcheckingifaddsucceeds

3.  Traversethelist,andforeachelementtraversethelistagaintoseeifitoccurselsewhere

Collec&ons.sort(bag);

booleandis&nct=true;

for(inti=0;i<bag.size()-1;i++){

dis&nct=dis&nct&&!bag.get(i).equals(bag.get(i+1));

}

§  Canalsoexitassoonasaduplicateisfound:for(inti=0;i<bag.size()–1&&dis&nct;i++){

dis&nct=!bag.get(i).equals(bag.get(i+1));

}

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Set<Integer>tmp=newHashSet<Integer>();


for(inti=0;i<bag.size();i++){

dis&nct=dis&nct&&tmp.add(bag.get(i));

}

§  Canalsoexitassoonasaduplicateisfound:for(inti=0;i<bag.size()&&dis&nct;i++){

dis&nct=tmp.add(bag.get(i));

}

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Collec&ons



for(inti=0;i<bag.size();i++){

intx=bag.get(i);

for(intj=0;j<bag.size();j++){

inty=bag..get(j);

dis&nct=dis&nct&&(i=j||x!=y);

}

}Canalsoexitassoonasaduplicateisfoundbyadding&&dis&ncttobothloopcondi&ons

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Iterator<Integer>outer=bag.iterator();


while(outer.hasNext()&&dis&nct){

Integerx=outer.next();

Iterator<Integer>inner=bag.iterator();

while(inner.hasNext()&&dis&nct){

Integery=inner.next();

dis&nct=!x.equals(y)||x=y;

}

}

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Givenalongsentence,findallitswords;thedis6nctones(regardlessofcase);displaythem;sortthem;andthenlocatethelongestandmostfrequentones.

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A"word"isdefinedasasequenceofcharactersterminatedbyspace,punctua6on,orend-of-string.

1.  Usesplitwitharegex2.  Turnarraytoacollec&on3.  Usecollec&onAPI

SeeWordSmith.java

§  Aniteratorisanobjectthatallowsyoutotraverseacollec&on

§  GivenareferencebagoftypeList<E>orSet<E>onecangetaniteratorforitasfollows:

Iterator<E>itr=bag.iterator();

§  Tocheckifthereisanextelementonecallsthebooleanmethoditr.hasNext()

§  Toobtainthenextelement(providedthereisone)wewrite

Ee=itr.next();

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Collec&ons


TheextendedforloopforareferencebagoftypeList<E>orSet<E>:

for(Ee:bag){

…

}

justabbreviates/standsfor

for(Iterator<E>itr=bag.iterator();itr.hasNext();){

Ee=itr.next();

…

}

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publicsta&cSet<E>intersect(Set<E>set1,Set<E>set2){

Set<E>result=newHashSet<E>();

for(Ee:set1){

if(set2.contains(e){

result.add(e);

}

}

returnresult;

} 18

publicsta&cSet<E>union(Set<E>set1,Set<E>set2){

Set<E>result=newHashSet<E>();

for(Ee:set1){

result.add(e);

}

for(Ee:set2){

result.add(e);

}

returnresult;

}

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Basic

size()

clear()

iterator()

Map

put(K,V),get(K),keySet()

containsKey(K)

containsValue(V)

List/Set

add(E)

remove(E)

contains(E)

ListOnly

add(int,E)

remove(int)

get(int)

OtherAPI

Theenhancedforloop

Collec&ons.sort(List)

Arrays…seeAPI

Collec&ons


§  AMap<K,V>isrepresentsamappingbetweenasetofkeys(oftypeK)andasetofvalues(oftypeV)

§  Eachelementinamapisakey-valuepair

§  Thekeysmustformasetandallbedis&nct

§  Thereare2classesthatimplementtheinterfaceMap<K,V>:TreeMap<K,V>andHashMap<K,V>

§  Usemap.put(k,v)toaddorupdateakey-valuepair

§  Usemap.get(k)toretrievethevalueassociatedwithkeyk

§  Othermethods:remove(k,v),containsKey(k),containsValue(v),keySet(),size(),toString(),etc.

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Map<String,Integer>m=newHashMap<String,Integer>();

m.put("John",23);

m.put("Mary",22);

m.put("Paul",19);

System.out.println("Maryis"+m.get("Mary"));

m.put("Mary",21);

System.out.println("Maryis"+m.get("Mary"));

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Map<String,Integer>m=newHashMap<String,Integer>();

m.put("John",23);m.put("Mary",22);m.put("Paul",19);

for(Stringk:m.keySet()){

System.out.println(k+"is"+m.get(k));

}

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Givenalongsentence,findallitswords;thedis6nctones(regardlessofcase);displaythem;sortthem;andthenlocatethelongestandmostfrequentones.

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A"word"isdefinedasasequenceofcharactersterminatedbyspace,punctua6on,orend-of-string.

1.  Usesplitwitharegex2.  Turnarraytoacollec&on3.  Usecollec&onAPI

SeeWordSmith.java

Collec&ons


§  SupposewewanttheinverseofaMap<K,V>m

§  Justtakingthesetofallpairsvalue-keysfrommdoesnotworkbecausethevaluesmaynotbeunique

§  Onesolu&onistocreateanewmapMap<V,List<K>>invwhichassociateseachvaluevinmtothelistofallthekeysthatmmapstov

§  E.g.inverseofthemap

{"John"=23,"Paul"=21,"Mary"=23}wouldthenbe{21=[”Paul"],23=["John","Mary"]}

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publicsta&cMap<Integer,List<String>>invert_all(Map<String,Integer>map){

Map<Integer,List<String>>result=newTreeMap<Integer,List<String>>();

for(Stringk:map.keySet(){

intv=map.get(k);

if(!result.containsKey(v){

List<String>list=newArrayList<String>();

list.add(k);result.put(v,list);

}else{

List<String>exis&ng=result.get(v);

exis&ng.add(k);

}}

returnresult;

} 26

§  Addressesques&onssuchasHowmuch&me(orspace)doesagivenalgorithmtakedependingonthesizeoftheinput?

§  ThatisifNisthesizeoftheinput,andT(N)istherunning&meofthealgorithmforaninputofsizeN,wewanttoknowhowT(N)growsasNgrows

§  E.g.HowlongdoesittaketosortalistofsizeN?§  Running&memaydependontheactualinputvalue(e.g.

list);usuallywesimplifybylookingattheworstcase

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§  Big-Onota&onisusedtocharacterizehowfasttherunning&meT(N)ofthealgorithmgrowsasthesizeoftheinputNgrows

§  T(N)isO(f(N))ifT(N)≤Cf(N)forallN≥KforsomeconstantsCandK

§  Thatis,ifT(N)isalwayslessthanf(N)mul&pliedbysomeconstantbeyondagivenvalueofN

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Collec&ons


§  TofindoutifanelementxiscontainedinanunsortedList<Integer>listwecandoalinearsearch:

intresult=-1;booleanfound=false;

for(inti=0;i<list.size()&&!found;i++){

inte=list.get(i);

if(e==x){

result=i;found=true;

}

}

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§  Thisisessen&allywhatthecontains()methoddoes

§  Therunning&meisO(N)whereNisthesizeforthelist

§  ThisisbecauseintheworstcasewehavetocheckandcomparealloftheNelementsofthelisttox

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§  Tosearchasortedlist,thereisamuchfasteralgorithm,binarysearch,whichisusedbyCollec&ons.binarySearch(List<E>l,Ex)

§  Comparexwiththemiddleelementofthelist:ifitisequalwearedone,andifitislesswecaneliminateallelementsa{erit,andsimilarlyifitisgreater;thenrepeatwiththeremainingpartofthelist

§  Soa{ereachcomparisonwecutdowntheremainingpartofthelistbyhalf

§  Sotherunning&meisO(lgN)whereNisthesizeforthelist

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§  Tosortalist,therearepre|yfastalgorithmssuchasquicksort,whichisusedbyCollec&ons.sort(List<E>l)

§  Therunning&meisO(NlgN)whereNisthesizeforthelist

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Collec&ons


ArrayList§  get(int)andadd(E)areO(1)§  add(int,E),get(E),contains(E),remove(E),andremove(int)

areO(N)

LinkedList§  get(int)isO(N)§  add(0,E)isO(1)

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TreeSet§  add(E)isO(lgN)§  contains(E)isO(lgN)§  remove(E)isO(lgN)

HashSet§  add(E)isO(1)§  contains(E)isO(1)§  remove(E)isO(1)

SimilarforTreeMapandHashMap

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7 8 9 collections - york university...add(e e) on a set returns false if e is already in it (for a...

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