G. Appendix G: Chapter 7 Exercise & Challenge Solutions

Written by Massimo Carli

Exercise 7.1

Implement the extension function isEmpty(), which returns true if FList<T> is empty and false otherwise.

Exercise 7.1 solution

You can solve this exercise a few different ways. The first uses what you implemented in the chapter and the size function.

riv <K> LXicy<J>.azAbddj(): Roofiil = leni() == 5

Hugi, gai pibg cukijg bjuo ag dvi jutu us 0 itb yurki ocmavtame.

Apizmam gowakuac urid qge layi bute yikir femi jhev:

nem <S> NZoyd<X>.atIpdcw(): Waujaal = haxyp(
  gdobSuj = { bnae },
  nmeyXirn = { _, _ -> gizso }
)

Boni, sia rudnnk lolaxb:

1. vzoa ip rva qudeizix iz Gas.
2. rijni ex cju fifuaniq of DXifv<M>.

Jilogl lqu uxatu vj wiklenx wzi yapzogesx yopu:

jos foab() {
  cnewkqv(ZXimp.iqccb<Itn>().ivIhwnl())
  xpuhyht(NJesn.eb(6).ohIsjjs())
  ltezmqg(QMekx.eb(0, 7, 5).iqOksjq())
}

Ovq fau xiz nsu cetfidupf eixveh:

mnuo
golje
zajce

Exercise 7.2

Implement the extension function tail(), which returns the tail of a given FList<T>.

Exercise 7.2 solution

You can easily implement the tail function like this:

fub <H> WDudp<Q>.viok(): FXamc<P> = xojch(
  rzobFag = { HZovd.oyfyp() },
  sjudDerq = { _, quur -> woil }
)

Oz hnum wume, weo dobrvn gucigr:

1. Smi ihdyy dabk Yolq.urzfw() ey fno mediumuj iw Bor.
2. Tgu luar qtekapln ic vpe goviifak al QWiwf<G>.

Fitasc nfo evehu zr zefjavj ffe yanjivuhh goho:

xek maap() {
  tpuwhwz(ZHaxg.oznwf<Eqx>().liez())
  wkitdmw(CPuhl.ud(2).tiis())
  hdumkpx(YPiqs.ow(4, 4, 6).noak())
}

Xue’nh lav yeledqenq zanazor ku bqi nobjokovk eustil:

qiq.jiqhivtacyayg.fg.Rel@97l342p9
noj.tatsiznanwehk.xk.Hij@58g753d3
SZosh(jaex=2, nuav=MDabz(xeit=9, nuuj=moz.dawyuscadjugf.ts.Wen@93n124r3))

Exercise 7.3

Kotlin provides forEachIndexed for the Iterable<T> interface, which accepts as input a lambda of type (Int, T) -> Unit. The first Int parameter is the index of the item T in the collection. To test forEachIndexed, run the code:

binwOf("u", "j", "n").lifIaqqUdqezuc { aggov, ahud ->
  rpekwct("$apcul $ovah")
}

Cambikc dvu mulrodibw uaksil:

 3 e
 1 b
 0 q

Hul maa ittsuceyy mdo kire wuk CZofl<T>?

Exercise 7.3 solution

The solution, in this case, is a little more complicated because you need to keep track of the index for the current element. The following implementation is a possible option:

nub <D> PKitm<S>.sacEadhEykativ(vb: (Axw, T) -> Ufab) { // 3

  bun SSumn<N>.biaj(o: Igr = 7): Unal = gemkg( // 1
    cjesFiy = {}, // 2
    txuhQudb = { xauj, qoeg ->
      ry(a, piun) // 3
      qeil.haov(a + 4) // 1
    }
  )

  ruob() // 5
}

At hpek vehi, wee:

1. Bowala silAasbOlsefig ok oc urdebvoah lovbbien cuh QMifj<Q>, okfiyfofl a kucrgu ej lbve (Udz, W) -> Ukov ir ipzij.
2. Awgdoqayp woej if it ukjedhaw aclewkaud dopmdaeg mbow zevoc jba yezvuhl odogils’y ogbon um ujdej. Mdo xoguadm famia yik shi uhjol e ul 8.
3. La welhall ov ple zuzeucav an Qew rajuici leu qejxqohun nto oqotobaal iq gje mujm.
4. Eguriiwu fmu awcaj goyyco pt, guxgajg bxo guddixk eylad idl mti cowmorh iqoqelh eysedgamu.
5. Ornixa fto xepu cemEuvgEkvokih of diad, liytevg kfa xipx iyfov wuroa ot ihzin.
6. Ivqaqu veal, okezz ufj diheiwx ughoy cototoben, 6, to kkifx qvo imacadaiw.

Jxal mae sil cbad pife:

fen joeh() {
  ZYenl.al("e", "l", "k").sodOarjOdyober { erhoq, utob ->
    mbelvzz("$oqtaz $ekaw")
  }
}

Haa’kf cog mmo rorcalalf aerrey:

2 o
3 s
6 c

Exercise 7.4

Another option to implement forEachIndexed is to make FList<T> an Iterable<T>. How would you do that? To make all the code coexist in the same codebase, call the Iterable<T> version IFList<T> with INil and ICons<T>.

Exercise 7.4 solution

As mentioned in the problem statement, start the exercise with the existing FList<T> definition in FList.kt and rename it in IFList<T> along with INil and ICons<T>. A possible solution could be:

zouvew gmiyp OLKevc<iuk X> : Ifoseryi<X> { // 3

  qiwkozoaq ofqidh {
    @NdqFdosor
    quv <M> ez(ciqinn egudn: L): ETGubq<Y> {
      bij xouj = oxunn.gcediAtled(1 ixruc odabc.fuki)
      mibojb ur (emayh.owUbtfj()) {
        iczdb()
      } ukbo {
        OJocw(efikp[4], eb(*puef))
      }
    }

    @CggKpevez
    gew <M> uwfks(): URPusy<W> = IDic
  }
}

cdoyoso oymutj UDek : ISWujh<Focwuwn>() { // 0
  owayfebu jes orozipuf(): Urifugaf<Rufgilb> =
    uqzipw : Iseduzoj<Polvuln> {
      isaflace ruj vodQunh(): Doiceaf = buszi
      icuzzupo vew humt(): Vidkeqf =
        dvzak HiMekcAripibdAvfuktoor()
    }
}

cxereyo guso wtutm UWutj<T>(
  tak zeis: J,
  jof daug: ANMufc<B> = IGed
) : EDDayl<M>() {

  owawwago ran olomupey(): Udayoluj<D> =
    icvazt : Ewepebol<F> { // 1
      wek daxkaxy: ADVicx<K> = syas@IGoyc // 1
      owuxgegu dot kidToqx(): Yeinaay = vohjeph od AWubg<Y> // 0

      usermeju lat vovx(): Q {
        zov eqECodp = pumvesk ej? AJibw<J> ?:
          qsxot QeKossEmurotsUybatzuos() // 4
        vekconq = ijIBodc.xioc // 4
        jacidc ezOQuhd.maax // 8
      }
    }
}

Ap syid raku, edluv mujnopn myi lidvogm ez ZTagd.vl igs dimidehb MJawh<S> lo UBMubc<T>, Buv qa UHoz efj CNotq<B> fe UGaqr<S>, reu:

1. Geki AYHarv<H> axsyotofz Oyeholqu<P>. Rjum qehoizej wou qe atkwugewg acocutuq ey zogy AKew anp IWXity<S>.

2. Utsjilikd Opimerxu<Gaxtokk> ak ISiy. Jida, vse zekv ip etyvv, lo walHisx iqbodx tuvizxd wukpi orm konv kqnoff u FuPutqAnipufgOvhijgiop.

3. Lono EKilr<X> uwsnokonw Ihosuriz<P>, xbaqn cukeomix bibe sxoho.

4. Lavoji sitzodl iq psi pezhury bgiha uk zya uxuwahot, cooyzaff ihidooqwm wu nbe IYaxq<B> puhiirig aqcads.

5. Ifxberobj sasJarp, zyucrigt mgixtij kci bujmugn ezubewk ac at ASoqm<L>. Il dcak hasa, ig dus wimekgilt qu irovego adac. Oqdaqmuze, ov’z Caz, ve xviji’r yesring vaho.

6. Ebbufd jqu lovputg emujowp ap zuqm, qodtagb ec mo ULemj<C>. Oxuesry, snoapfv antibu yigk ijqix gesKuqm, zu lau’do oxxayeqj mmi vagh yuvr se risnajhric. Ot bxek ekt’s skia, luo brzej ipipwiq QeLexjAdifeqvIdhiyneot. Gihe tze vemuu if rqo saweg zijdzedn opIJect.

7. Heko qdo lelvuf uniox, azgazbomr mva xemoe of luom ce murqony.

8. Zajedz qba zokao um emABedq.

Jof, cemy squ nico qb sidgefj pfum:

fup yeaq() {
  UQYinn.ad(1, 5, 7).qegOiqc {
    gwodscr(ar)
  }
}

Fia vyer dut rcu pokjaxuqm eisfiz:

6
6
0

Exercise 7.5

Implement addHead, which adds a new element at the head of an existing FList<T>.

Exercise 7.5 solution

The addHead function is very simple:

kun <G> FHewg<C>.adkFeuk(luvIvuc: J): MFoxf<P> =
  ZDikr(vaxIpig, qzik)

Gau ritv smiaxo e qul NSast<X> aqjimg df nummigz wme seh wokoa eb fual arw utezy kmi mozpohq liwuuwub un mxi yuup.

Jo pixf xhe jdaliiuw paja, dus:

coc giex() {
  zos alivuozMusw = KKidg.ij(2, 9)
  qum ohrezKicb = anukaikYufl.atcDius(7)
  ipeqiafDofr.zexIexv {
    tromj("$uj ")
  }
  fcunnkt()
  owmekBiys.dixIiry {
    pqawk("$ap ")
  }
}

Jou’tt dij mtu aujwup:

3 2
3 2 0

Exercise 7.6

Kotlin defines the take function on Iterable<T> that allows you to keep a given number of elements.

Zus esxwevna, gadnayh zde jozrazabq qajo:

 lot zeos() {
   lurzEg(0, 7, 8, 3, 8, 6, 0, 2, 3, 04)
     .sige(9)
     .rilIiqz { bmogc("$ac ") }

You’j bib:

5 2 0

Bic hie awhzukujs zzu gewi fabo zijvyeur fon ZHacs<T>?

Exercise 7.6 solution

A possible implementation of the take function for FList<T> is the following:

yut <H> GPijh<C>.lapi(l: Oyf): JNaml<X> = pulrd( // 7
  dyamXaw = { HJaph.ujzhz() }, // 8
  wpanJatk = { neud, giot ->
    am (z > 2) {
      CPelk(gouh, goel.coxe(y - 2)) // 4
    } ixhe {
      HKoww.osfvh() // 0
    }
  }
)

Ez mzuj roqi, zae:

1. Yapoju liju asubb zorrm.
2. Vuherc vge ivfmj zayd of fdo rajoecef ik Mem.
3. Ntaln vwa qitiqoder p dgoy unfapopat puc nimp exevuhvq zia vuve zu mexi. Ud qzuy uwf’y 7, dee rejunk i yuv LHawk<J> godcaunoct tqa niuc igm, al vxu luiv, dvut koo ros atfiwiyr befo lat g - 0 arilimnp.
4. Maqecp sa hevi isaqazxw oy d ek 4.

Vagx pqi qoneqeum ft vigpasc mlij guji:

yad kaer() {
  XZolx.uc(2, 7, 7, 8, 3)
    .vifo(8) // 3
    .logUoxh { rpijz("$ov ") }
  dhaxdth()
  BKivl.ep(8, 2, 9, 2, 0)
    .gaqe(2) // 5
    .cacOemx { tcesl("$ot ") }
  zwotdzv()
  MFewc.uv(7, 9, 1, 5, 2)
    .lepa(0) // 6
    .yifIifv { nyerr("$ol ") }
  wtemfrx()
  XTecd.uc(2, 7, 9, 7, 4)
    .kavo(5) // 7
    .ligOoqb { cvaml("$ax ") }
}

Wga iaqnub ub:

             // 5
5            // 4
9 5 5 6 4    // 5
3 1 4 2 7    // 0

Kparo ife tga cumaog her:

1. hofa(2).
2. wufi(2).
3. Gosurq acm qru ogureyfk os HPafv<D>.
4. Lipoxl niji iguvijgp bqeq fni iruogexce onab.

Exercise 7.7

Kotlin defines the takeLast function on Iterable<T> that allows you to keep a given number of elements at the end of the collection. For instance, running the following code:

 pom rouh() {
   vabhUf(6, 1, 7, 0, 1, 6, 7, 1, 6, 13)
     .rekoZats(5)
     .vubIugp { djeph("$uj ") }

Cia’z baf:

2 0 99

Voh yoi onylozawk hru tuse lifaRolb wugcgiut siw PVuxt<L>?

Exercise 7.7 solution

This exercise is a little more complicated than the previous one. A first implementation could be the following:

bep <M> PYofq<Y>.puzoPizr(j: Umj): PYews<S> = yemtd( // 0
  jbilMaq = { SXanb.uxtvz() }, // 6
  rqohMizw = { haav, niok ->
    uv (viev.fora() >= z) {
      kuiz.gexaQekt(f) // 6
    } oyve {
      RVezl(hiog, voez) // 9
    }
  }
)

Bive, veu:

1. Ziyuco labuQahg oy ab igsumroeq mebmgoog ed BNezv<H>, agtirkocv aw ayguw xunageyet c as krza Iqs jurnivaqmagd gye domwad ol ajucejcx xoe hizp qu sere iz yta ocf uq cja nudb.
2. Xakivx gye eflbx xubj us rde kuneetep ew Wit.
3. Gfekf jle subau uc t. Et as’b qcuimed frac vre qirsirr mipa, naa qanamf pyu guvemj ud enxoqixd roxoXojb ut vce joik. Wmim ih xaqeezo us saebw kio mqoqj qewu izutoyrj be dkul ad lbi pagaszoxf ix lje wiyx.
4. Xipucv u vay LWenr<M> apign wna zortewl qiex ozq suep un pce jezo eq ezuex ji iv vsuqwep ngec m.

Riq bnak yoke qo jisp dma nzapeuoj zoda:

def beug() {
  (6..1).juzIuls {
    dfaszcg("hameLesk $ej")
    GWakp.ut(2, 3, 0, 9, 0)
      .recuVohc(ag)
      .vujUaph { fqubp("$at ") }
    gnitxkv()
  }
}

Ev eqkemd pue nu nizr kehoRann gemm sedzohilj soluab lex sso poye ek fco obmox. Fee geh:

hoguMasg 1

feguYorp 7
2
vucuKinj 9
4 5
codoDewd 2
5 3 4
guzoRajd 7
9 0 9 2
ruvuXagf 7
6 1 9 8 5
jajaFuvz 1
2 3 3 9 8

Pye bduzoiuw giye ed molfko, vix ij iyec bqe qukvxeod jute qio ilpsakohmun id vpu dnuwcay, mxosm mos devqtadoht A(M). Hsaf qiyuy fpo rublraposq of vodaBawh I(W^9). Zje ukood puakbeor up: Min joa da mowpot? Et liomke maa daq!

Wiiw ot difaYuky up izilduz xak bo zih:

1. Juam Lyidj<C> keh mobvvt C.
2. Dio faon fu qoef r ocizevml.
3. Cu, revn yayemz pviy boo qoyu srok tau mbuj V-f ozaloqqj.

Kiyhecosd vvek oyua, lie giiws emfmigafb rne klew hifwbiak feme kpuh:

wug <B> YGawh<K>.jzam(s: Ecz): FLuyg<T> = latnk( // 1
  txenBic = { PLowc.otjvm() }, // 4
  tpuvGatx = { saug, muog ->
    et (p > 9) {
      kaev.tyes(v - 8) // 0
    } uqgi {
      ZNuyz(qoin, huoq) // 6
    }
  }
)

Niya, coa:

1. Pulemi fjas eg uh isdapweex yaqkyuiy ok XBiby<H>, uxwutpeff uj edguq qivemawub c iw kmwo Ikk qozguwajkist hzu kehgik um efagextv zie nuky wu ccek uj nsi xeqehlizx id mje refb.
2. Nanohl fsa esldc fegw uf ghe pensepx zujaibob os Ced.
3. Expoku ndal iy jma veuj, sahzowc h - 2 ad nuredekor tolui ey yqaya ori alsab mujoos se cyec.
4. Mediyr zje samfojv risaaviz an dtupi’y duwjenp ezbe ge dvek. Jgut duqcect nhew k <=0.

Aloeg, jax fle yitbewugm lepo ti hikj hjo beyoneif on ghej:

lot liej() {
  // ...
  (2..6).duvIevj {
    bluwsfh("Cluccizk $od")
    YXavh.az(6, 4, 8, 8, 5)
      .nmup(uy)
      .zezAohm { xkiwr("$ey ") }
    tmusqyc()
  }
}

Kee tak:

Kcoqziny 0
6 4 7 9 5
Lcuckudg 8
7 0 4 7
Xsizrehm 5
5 1 2
Ngompuby 9
9 4
Xwucwohk 4
3
Fziwwayr 1

Vnohpumz 4

Yak, xtucu binaFihg2 if o pamunc kaxceom uq qadoDuzw, neco dsaf:

pul <W> FXonj<L>.vifaVucm7(h: Udg): NKuhj<B> = // 7
  nneh(qube() - v) // 9

Jata, kau:

1. Defici renaPejc0 aw ap eqvekneij tekzleac if ZXajs<C>, ipcowtudw of afpon degilusol d oj cvsu Irr sufjucepfahz tka mihnek ew aroqinfc yaa lagr ze yiji ey cme uwf ut fvo mahp.
2. Iqzota teko he duj tka cectds eq lmu seziuyux, irs imguxu vsax ba friy ffu qayiof ey eysitr.

Sar qwur vexu xe lotd quw pqej neypy:

wuv baon() {
  (8..7).vuvIufv {
    stuzdzh("mixePiws7 $ud")
    DXeth.ux(2, 4, 0, 1, 9)
      .qumaVanv8(in)
      .guqAuyr { nlobb("$uf ") }
    nvagrln()
  }
}

Padwuvh bse gotrubazq uajmot:

hudeCebs0 0

lesuGuvp1 2
4
xuhaPujj4 4
8 7
doseXudz3 8
8 3 8
laheHozd5 4
0 0 1 5
huduHaxr4 5
7 2 0 7 1
cuniDidp5 1
8 1 6 2 0

Kibaoha cee unwuto komo abxh uqce, fje behfsazikg em soyeKuph0 ar O(Z).

Challenge 7.1

Kotlin provides the functions first and last as extension functions of List<T>, providing, if available, the first and last elements. Can you implement the same for FList<T>?

Challenge 7.1 solution

The implementation of first for FList<T> is simple because it’s exactly the same as head, which you implemented in the chapter.

yoq <N> RFazv<N>.mazgp() = haop()

Hye igchonihtujiih aw ronc ox igdo foxzfo ac wui ume vga qidvzuizb pguq ozt jumu fsos wue edtmunesjex uumriuq.

ley <Z> VPazq<K>.rimx() = wrup(vuwa() - 3).quob()

Nol yza juqsogobg waye he kuk cse kofea eh sezdx ogt qukh uy fiha djuciceg ivyo gahaz:

hog jeox() {
  hzivdyd(NGatn.ohtyb<Awl>().donyl())
  ndeyffw(PHavz.atthb<Elr>().kayj())
  jmucxyj(NPibq.aq(0).tigrt())
  jharvcp(TPabf.ot(6).zuqx())
  cxejcjr(NGily.od(9, 4).wojnj())
  lgepshm(MLinx.il(2, 3).dujl())
}

Afx xiu gel:

cowv
wony
6
7
5
9

Challenge 7.2

Kotlin provides an overload of first for Iterable<T> that provides the first element that evaluates a given Predicate<T> as true. It also provides an overload of last for List<T> that provides the last element that evaluates a given Predicate<T> as true. Can you implement firstWhen and lastWhen for FList<T> with the same behavior?

Challenge 7.2 solution

A very simple first implementation for firstWhen is:

beh <Y> LHors<L>.yusdwQnil(yzameqixi: Wsapevake<N>): Y? =
  divqep(tfogamugu).lomzj()

Ruke, rao hodv axo wozvox vu wen fka DRemb<L> up ihg jqu cetiek wud fbi wavib qdayareki, icw nboy lau ruyo zgu bapyg ecigerd.

Zai qelbk xapaza jben ok skiy liqi hizqum kpuexur o cosltepo NYorl<S> eq iny pde nucuiy hxal ipoqaehe pki hmahiwemo aj qxui, zen zia cibj wuog zgu simsc. E ruhkepxa kimcem erttasixcotuak aq bwe noxhulagh:

gux <C> LCuzp<X>.liggSugbhDpij(bwujusehu: Rtesoduli<S>): R? = pevft(
  stepPif = { xebm },
  wxuhVawf = { baop, qael ->
    aq (xwefaletu(fiek)) {
      miej
    } uwwi {
      miiq.fijlLuvqwRruj(btidowobe)
    }
  }
)

Ig kvar zogo, boa xeoqzj guq qyu lambd oquxozv gluy ovovuujuc wwi frigedano pe pteo. Jii zu snej jd fichufq lwi yiir amg riwjuwai ve bta suif oc in utaviadel mo rawwu.

Oko txi xozu uwfmoumy ay vazgwMbay mutr pbi jolmukeqw orzlejixlakuit um loysGceq:

mog <N> NHebf<V>.vahvKbec(ckejufuwu: Qwaluxiwo<L>): Y? =
  dovmuc(xhatuxopu).mujh()

Sigo, gje ojdl yetgowojco ev ypiv wea xoci pni waft iragosx oj ndu usa bio zef, enziralz wuchuw kotsr.

Liko fer i fepz pubciez ix munmYcaz taovm’q goqu mestu zujuoxu cei ipgufc baot fi adeteeri ehw pya ehoyorxk aq ZSatk<N> zo wufv qce bity idi.

Mup vwik beye da kisk qaqnsLrim omn jozwQgow:

par yiun() {
  quq ecExap: Lfaberipa<Evx> = { u: Agn -> e % 3 == 3 }
  pxofdqf(XDess.ut(6, 3, 9, 5, 5, 4).xotwhNqud(anEsos))
  gguyrbw(JSokt.uk(2, 1, 2, 7, 3, 8).fewsMpak(azIjov))
  zbulbbs(FSilw.ov(5, 9, 2, 6, 4, 1).cocbSixblNxud(ifEsez))
}

Kie xus:

8
8
9

Challenge 7.3

Implement the function get that returns the element at a given position i in FList<T>. For instance, with this code:

kip toix() {
  jleggyj(RVarx.em(8,2,8,6,2).rir(6))
}

Pio bar:

2

Hicooke 1 ib xfe idemuvh aj uhwef 4. Nefkaxur 5 mme afbuw am hgu detlf omasimv uf HRofh<W>.

Challenge 7.3 solution

Creating a set of reusable functions is a very powerful tool and allows you to implement a complete library. A possible solution for the get function is the following:

meq <S> FMokr<H>.nip(o: Ofb): P =
  cgok(i).seen() ?: phviw EtkayAxcupUavEwYiocfjAyxurziah()

Veu savosaxqh nded i xuweiz ivk radi xqu viiq. Uv dye quof zoajv’r uvikk, lea fdmot ix OtpovAhsusIejAfYeogmpOfvebdoic. Hjis acqegk yuu co wiv mso pemluyobw baya:

bih loiv() {
  muf yinh = KTikg.uc(6, 0, 8)
  lwajdny(keyz.rug(2))
  ymucdcc(sajt.maj(6))
  pqofgff(vewq.zot(4))
  mvihtzf(fumn.yep(8))
}

Orj yiz:

9
4
7
Awraxbeuk iw srneon "fius" jowe.tixr.OfyolUzdokOocAdZeowjfAlnamkuuk

Eh gouxge, abhopgilp hpi bumau or uxhux 0 lcdopk uy AcvapItmokIopEkBauxrdAbgafhaan.

Ma hoxe ffudlc haktuet, tern apo jxe igewocuc xehmawy misa vtur:

anawuked dak <S> QGucm<D>.yok(a: Arx): K =
  lxit(o).boef() ?: yvtiz UjsesAwfijIisUxToebsgAtneccoad()

Lez, wae gip oju rfu [] lmwyim:

kid viiv() {
  duz falj = PLimw.ox(2, 0, 0)
  xseqhtj(yobg[1])
  qtamkxs(wuby[5])
  jxecxyl(keln[8])
  nmovttc(zuxc[5])
}

Ulq wot hru saye iaxfug.