Objectives. Two Ways to Implement Lists. Lists. Chapter 24 Implementing Lists, Stacks, Queues, and Priority Queues

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1 Chaptr 24 Implmnting Lists, Stacks, Quus, and Priority Quus CS2: Data Structurs and Algorithms Colorado Stat Univrsity Original slids by Danil Liang Modifid slids by Chris Wilcox Objctivs q To dsign common faturs of lists in an intrfac and provid sklton implmntation in an abstract class ( 24.2). q To dsign and implmnt a dynamic list using an array ( 24.3). q To dsign and implmnt a dynamic list using a linkd structur ( 24.4). q To dsign and implmnt a stack class using an array list and a quu class using a linkd list ( 24.5). q To dsign and implmnt a priority quu using a hap ( 24.6). 1 2 Lists Two Ways to Implmnt Lists A list is a popular data structur to stor data in squntial ordr. For xampl, a list of studnts, a list of availabl rooms, a list of citis, and a list of books, tc. can b stord using lists. Th common oprations on a list ar usually th following: Rtriv an from this list. Insrt a nw to this list. Dlt an from this list. Find how many s ar in this list. Find if an is in this list. Find if this list is mpty. Thr ar two ways to implmnt a list. Using arrays. On is to us an array to stor th s. Th array is dynamically cratd. If th capacity of th array is xcdd, crat a nw largr array and copy all th s from th currnt array to th nw array. Using linkd list. Th othr approach is to us a linkd structur. A linkd structur consists of nods. Each nod is dynamically cratd to hold an. All th nods ar linkd togthr to form a list. 3 4

2 Dsign of ArrayList and LinkdList For convninc, lt s nam ths two classs: MyArrayList and MyLinkdList. Ths two classs hav common oprations, but diffrnt data filds. Th common oprations can b gnralizd in an intrfac or an abstract class. Prior to Java 8, a popular dsign stratgy is to dfin common oprations in an intrfac and provid an abstract class for partially implmnting th intrfac. So, th concrt class can simply xtnd th abstract class without implmnting th full intrfac. Java 8 nabls you to dfin dfault mthods. You can provid dfault implmntation for som of th mthods in th intrfac rathr than in an abstract class. java.util.itrabl java.util.collction MyList MyArrayList MyLinkdList «intrfac» java.util.collction<e> «intrfac» MyList<E> +add(indx: int, : E) : void +gt(indx: int) : E +indxof(: Objct) : int +lastindxof(: E) : int +rmov(indx: int) : E +st(indx: int, : E) : E Ovrrid th add, isempty, rmov, containsall, addall, rmovall, rtainall, toarray(), and toarray(t[]) mthods dfind in Collction using dfault mthods. MyList Intrfac Insrts a nw at th spcifid indx in this list. Rturns th from this list at th spcifid indx. Rturns th indx of th first matching in this list. Rturns th indx of th last matching in this list. Rmovs th at th spcifid indx and rturns th rmovd. Sts th at th spcifid indx and rturns th bng rplacd. MyList Run 5 6 Array Lists Array List Animation Array is a fixd-siz data structur. Onc an array is cratd, its siz cannot b changd. Nvrthlss, you can still us array to implmnt dynamic data structurs. Th trick is to crat a nw largr array to rplac th currnt array if th currnt array cannot hold nw s in th list. Initially, an array, say data of Objct[] typ, is cratd with a dfault siz. Whn insrting a nw into th array, first nsur thr is nough room in th array. If not, crat a nw array with th siz as twic as th currnt on. Copy th s from th currnt array to th nw array. Th nw array now bcoms th currnt array

3 Insrtion Bfor insrting a nw at a spcifid indx, shift all th s aftr th indx to th right and incras th list siz by 1. Dltion To rmov an at a spcifid indx, shift all th s aftr th indx to th lft by on position and dcras th list siz by 1. Bfor insrting at insrtion point i 0 1 i i+1 k-1 k Bfor dlting th at indx i 0 1 i i+1 k-1 k Insrtion point shift data.lngth -1 Dlt this shift data.lngth -1 Aftr insrting at insrtion point i, list siz is incrmntd by i i+1 i k k+1-1 Aftr dlting th, list siz is dcrmntd by i k-2 k-1-1 insrtd hr data.lngth -1 data.lngth Implmnting MyArrayList Linkd Lists -data: E[] -siz: int «intrfac» MyList<E> MyArrayList<E> +MyArrayList() +MyArrayList(objcts: E[]) +trimtosiz(): void -nsurcapacity(): void -chckindx(indx: int): void MyArrayList Array for storing s in this array list. Th numbr of s in th array list. Crats a dfault array list. Crats an array list from an array of objcts. Trims th capacity of this array list to th list s currnt siz. Doubls th currnt array siz if ndd. Throws an xcption if th indx is out of bounds in th list. TstMyArrayList Run Sinc MyArrayList is implmntd using an array, th mthods gt(int indx) and st(int indx, Objct o) for accssing and modifying an through an indx and th add(objct o) for adding an at th nd of th list ar fficint. Howvr, th mthods add(int indx, Objct o) and rmov(int indx) ar infficint bcaus it rquirs shifting potntially a larg numbr of s. You can us a linkd structur to implmnt a list to improv fficincy for adding and rmoving an anywhr in a list

4 Linkd List Animation Nods in Linkd Lists A linkd list consists of nods. Each nod contains an, and ach nod is linkd to its nghbor. Thus a nod can b dfind as a class, as follows: Nod 1 Nod 2 Nod n class Nod<E> { E ; Nod<E> ; 13 public Nod(E o) { = o; 14 Adding Thr Nods Th variabl rfrs to th first nod in th list, and th variabl rfrs to th last nod in th list. If th list is mpty, both ar. For xampl, you can crat thr nods to stor thr strings in a list, as follows: Stp 1: Dclar and : Adding Thr Nods, cont. Stp 2: Crat th first nod and insrt it to th list: = nw Nod<>("Chicago"); = ; Aftr th first nod is insrtd insrtd "Chicago" : Nod<String> = ; Nod<String> = ; Th list is mpty now 15 16

5 Adding Thr Nods, cont. Stp 3: Crat th scond nod and insrt it to th list: Adding Thr Nods, cont. Stp 4: Crat th third nod and insrt it to th list:. = nw Nod<>("Dallas"); "Chicago" "Dnvr" "Dallas". = nw Nod<>("Dnvr"); "Chicago" "Dnvr" : =.; "Chicago" : "Dnvr" : =.; "Chicago" "Dnvr" "Dallas" : Travrsing All Elmnts in th List Equivalnt for loop Each nod contains th and a data fild namd that points to th nod. If th nod is th last in th list, its pointr data fild contains th valu. You can us this proprty to dtct th last nod. For xampl, you may writ th following loop to travrs all th nods in th list. Nod<E> currnt = ; whil (currnt!= ) { Systm.out.println(currnt.); currnt = currnt.; Th whil loop on th prvious pag can just as asily b writtn as a for loop, as shown blow: for(nod<e> nod = ; nod!= ; nod = nod.) { Systm.out.println(nod.); 19 20

6 MyLinkdList Implmnting addfirst(e ) Nod<E> : E : Nod<E> Link 1 m 1 MyLinkdList<E> -: Nod<E> -: Nod<E> -siz: int +MyLinkdList() Crats a dfault linkd list. +MyLinkdList(s: E[]) Crats a linkd list from an array of s. +addfirst(: E): void Adds an to th of th list. +addlast(: E): void Adds an to th of th list. +gtfirst(): E Rturns th first in th list. +gtlast(): E «intrfac» MyList<E> +rmovfirst(): E +rmovlast(): E Th of th list. Th of th list. Th numbr of s in th list. Rturns th last in th list. Rmovs th first from th list. Rmovs th last from th list. public void addfirst(e ) { Nod<E> nwnod = nw Nod<>(); nwnod. = ; = nwnod; siz++; if ( == ) = ; A nw nod to b insrtd hr +1 (a) Bfor a nw nod is insrtd. +1 MyLinkdList TstMyLinkdList Run Nw nod insrtd hr (b) Aftr a nw nod is insrtd public void addlast(e ) { if ( == ) { = = nw Nod<>(); ls {. = nw Nod<>(); =.; siz++; Implmnting addlast(e ) +1 (a) Bfor a nw nod is insrtd. +1 (b) Aftr a nw nod is insrtd. A nw nod to b insrtd hr Nw nod insrtd hr 23 Implmnting add(int indx, E ) public void add(int indx, E ) { if (indx == 0) addfirst(); ls if (indx >= siz) addlast(); ls { Nod<E> currnt = ; for (int i = 1; i < indx; i++) currnt = currnt.; Nod<E> tmp = currnt.; currnt. = nw Nod<>(); (currnt.). = tmp; siz++; currnt A nw nod to b insrtd hr A nw nod is insrtd in th list currnt tmp +1 tmp +1 (a) Bfor a nw nod is insrtd. (b) Aftr a nw nod is insrtd. 24

7 public E rmovfirst() { if (siz == 0) rturn ; ls { Nod<E> tmp = ; =.; siz--; if ( == ) = ; rturn tmp.; Implmnting rmovfirst() Dlt this nod (a) Bfor th nod is dltd. +1 (b) Aftr th first nod is dltd public E rmovlast() { if (siz == 0) rturn ; ls if (siz == 1) { Nod<E> tmp = ; = = ; siz = 0; rturn tmp.; ls { Nod<E> currnt = ; for (int i = 0; i < siz - 2; i++) currnt = currnt.; Nod tmp = ; = currnt;. = ; siz--; rturn tmp.; 1 1 Implmnting rmovlast() -2 (a) Bfor th nod is dltd (b) Aftr th last nod is dltd currnt -1 Dlt this nod Implmnting rmov(int indx) public E rmov(int indx) { if (indx < 0 indx >= siz) rturn ; ls if (indx == 0) rturn rmovfirst(); ls if (indx == siz - 1) rturn rmovlast(); ls { Nod<E> prvious = ; for (int i = 1; i < indx; i++) { prvious = prvious.; Nod<E> currnt = prvious.; prvious. = currnt.; siz--; rturn currnt.; prvious currnt Nod to b dltd (a) Bfor th nod is dltd. prvious (b) Aftr th nod is dltd. currnt. currnt. Tim Complxity for ArrayList and LinkdList Mthods MyArrayList/ArrayList MyLinkdList/LinkdList add(: E) add(indx: int, : E) clar() contains(: E) gt(indx: int) indxof(: E) isempty() lastindxof(: E) rmov(: E) siz() rmov(indx: int) st(indx: int, : E) addfirst(: E) rmovfirst() 27 28

8 Circular Linkd Lists A circular, singly linkd list is lik a singly linkd list, xcpt that th pointr of th last nod points back to th first nod. Doubly Linkd Lists A doubly linkd list contains th nods with two pointrs. On points to th nod and th othr points to th prvious nod. Ths two pointrs ar convnintly calld a forward pointr and a backward pointr. So, a doubly linkd list can b travrsd forward and backward. Nod 1 Nod 2 Nod n Nod 1 Nod 2 Nod n prvious prvious Circular Doubly Linkd Lists A circular, doubly linkd list is doubly linkd list, xcpt that th forward pointr of th last nod points to th first nod and th backward pointr of th first pointr points to th last nod. Stacks A stack can b viwd as a spcial typ of list, whr th s ar accssd, insrtd, and dltd only from th nd, calld th top, of th stack. Nod 1 Nod 2 Nod n prvious prvious prvious 31 32

9 Quus A quu rprsnts a waiting list. A quu can b viwd as a spcial typ of list, whr th s ar insrtd into th nd () of th quu, and ar accssd and dltd from th bginning () of th quu. Stack Animation Quu Animation Implmnting Stacks and Quus Using an array list to implmnt Stack Us a linkd list to implmnt Quu Sinc th insrtion and dltion oprations on a stack ar mad only at th nd of th stack, using an array list to implmnt a stack is mor fficint than a linkd list. Sinc dltions ar mad at th bginning of th list, it is mor fficint to implmnt a quu using a linkd list than an array list. This sction implmnts a stack class using an array list and a quu using a linkd list

10 Dsign of th Stack and Quu Classs Thr ar two ways to dsign th stack and quu classs: Using inhritanc: You can dfin th stack class by xtnding th array list class, and th quu class by xtnding th linkd list class. Composition is Bttr Both dsigns ar fin, but using composition is bttr bcaus it nabls you to dfin a complt nw stack class and quu class without inhriting th unncssary and inappropriat mthods from th array list and linkd list. Using composition: You can dfin an array list as a data fild in th stack class, and a linkd list as a data fild in th quu class MyStack and MyQuu Exampl: Using Stacks and Quus GnricStack<E> -list: java.util.arraylist<e> +GnricStack() +gtsiz(): int +p(): E +pop(): E +push (o: E): void +isempty(): boolan GnricStack An array list to stor s. Crats an mpty stack. Rturns th numbr of s in this stack. Rturns th top in this stack. Rturns and rmovs th top in this stack. Adds a nw to th top of this stack. Rturns tru if th stack is mpty. Writ a program that crats a stack using MyStack and a quu using MyQuu. It thn uss th push (nquu) mthod to add strings to th stack (quu) and th pop (dquu) mthod to rmov strings from th stack (quu). GnricQuu<E> GnricQuu TstStackQuu Run -list: LinkdList<E> +nquu(: E): void Adds an to this quu. +dquu(): E Rmovs an from this quu. +gtsiz(): int Rturns th numbr of s from this quu

11 Priority Quu A rgular quu is a first-in and first-out data structur. Elmnts ar appndd to th nd of th quu and ar rmovd from th bginning of th quu. In a priority quu, s ar assignd with prioritis. Whn accssing s, th with th highst priority is rmovd first. A priority quu has a largst-in, first-out bhavior. For xampl, th mrgncy room in a hospital assigns patints with priority numbrs; th patint with th highst priority is tratd first. MyPriorityQuu TstPriorityQuu Run 41