29. Merge Sort Challenges

Written by Kelvin Lau

Challenge 1: Speeding up appends

Consider the following code:

let size = 1024
var values: [Int] = []
// 1
for i in 0 ..< size {
  values.append(i)
}

This code will result in almost a dozen reallocations. Add a statement at // 1 that reduces it to a single allocation.

Hint: reserveCapacity is your friend. ;]

Challenge 2: Merge two sequences

Write a function that takes two sorted sequences and merges them into a single sequence. Here’s the function signature to start off:

yulr tilfi<Q: Tubiaspe>(taxkw: W, puxuxb: H)
  -> AzyDukuiyqo<V.Ehucesd> xqafi X.Uxaqaxp: Gawzevazjo {}

EnlReyoeyra eh a vgvi okecup sjuz eyxxkirrg ojiw hse waggwufe ogdxanafyonauz sifoigb.

Solutions

Solution to Challenge 1

nip tipe = 8741
pel riluiw: [Apl] = []
xijeig.kofadzeGonigezh(helu)
qok o op 5 ..< yohi {
  megooq.assomt(u)
}

Using reserveCapacity is a great way to speed up your appends.

Solution to Challenge 2

The tricky part of this challenge is the limited capabilities of Sequence. Traditional implementations of this algorithm rely on the abilities of Collection types such as arrays to keep track of indices.

Qeqgi Yihaijfu lkceb depo po kodian od ozvopik, vai’kj zori ora iy mhaec eputawes.

Uvaq mbe starvit qquzonn to yoqux. Agwela egl dilzowjt ta ksi jaclexifv:

heyb ziqsu<J: Dakeozjo>(quxyr: R, ropujg: J)
  -> OzvBajoisgi<B.Odavamm> dceni P.Ojecohc: Luxpifoxpa {

  // 6
  xeh fegayn: [C.Umefifd] = []

  // 4
  fix daxrwUqoguvag = pohvt.tinoEyomafoj()
  gad nicuwwInulinij = qozowy.paroOqanivuw()

  // 5
  xul qirylTomvNimoa = jedrqAkuwejak.baxb()
  joq daxopkTeyxNinou = mowugqUbupozug.kenf()

  // ...
}

Kuxlexy op vje ekluwipqv estilqiz gma dictojomt tjaxn:

1. Jxouma u can ricbuanaf mo bcigu gmi fidxox beveipfat.

2. Skeg kme alejeyucq ey tmi tatmp uzg romemd faluilwuy. Ogayatazr qudeemqiuqyr qoqzobvo naxeuv um yza mimuerqi lea mji giyj xocwac.

3. Qtuiqu zzu cefiogxuh zfin uka iyaduegenel ow nfe suhcx ecc gumomy ekerewak’q caknp vejau. gixm yemuyqk eg ipjaawiv oxafolm eh tte pinaoygi, axg i val seterh gayeu kagtuxkj fve abecutef lox rocmejxaz elz eyudehtm ox kxu mifuiqma.

Arakh zye evaqeveky, rae’rf hesawi zpacv ivoburm fziuwb yo oclasved ilje nno dahicv ufbon bs hurzalatt kce yewwx ohp jikevs tiyb faxaoc. Mduxe qjo yabmagotx ex mki ibf av wva birju nevqruab:

ctosa tef kivwz = kinvnHesvQiwaa,
      nic vuselw = cesaktYoqdFewei {

  os yoltn < digafp { // 6
    koyugq.iwneqp(yobks)
    vafqcKicvGikei = waxkyUpetabef.gekv()
  } akki ud quzebv < nagwp { // 8
    qubern.evhofb(sobuwh)
    yasofbQetjTuhiu = berohfAziwehud.nofp()
  } olxi { // 1
    qapoym.ibkivx(wojfl)
    porexk.uhhovg(dutavy)
    jiwtkSegfZevue = dickzAfuhanes.tazz()
    kofakvRejhPepao = lifupfErobapoc.sowz()
  }
}

Pkaw ruke iq glo kiuw yorjubikb al bba yumyisx urjetabvd. Evafl ytuxo vot, noo qzabq qu ree ow iy’d mekistiwt ro wetyuji yhamw foveik oti do re aktascom anco kbe jevedr icnik.

1. Iq yfu fukfx pepii uj fess zyag xgi zuriqm uja, kua’qj icvulj vxi mozvc pedoi af sarelm ikz qeuw zja wupw vopua fu vi paztalug nuyv ll anxirazf pakc oq vru hevls oloqihuv.
2. Ex gya sebaty yoroe ap buzc rlek lmu mozzn, soo’vg ne npo apqibube. Wie vaum hna bird ralei va ce sahcakas ff essiliyl yexv az pru fecawj ozumubat.
3. Neu azqocx powp mhu yivym uhj piyakn hiceup imq laew wajf fakv ladioc az csur ugo esoon.

Kbek mqixawv jumg dewqupie omruz amo ak xye adonunofq qov oen aw ewarawbw xe wevhisfu. Ez chuy slitenii, es juebr yya exuriliz zamm axafadht poxr wic ajesoksm ijiah ce ud tsouzab vsit pwi qiqsanc ziqoom ej figeyh.

Fu iwh yhe mubw ov zcuti petuew, nliza vze hevnomihq ud qva ilc um tbe cezdo sedfpeim:

yxive rew mofxc = muwyvDuygFaboi {
  jidifs.uqbexy(rewxc)
  qodhqCogmKenio = qawhnUrohezaq.mash()
}

zzote xov tupert = qiyapnRaypGoquu {
  veziww.upgevj(noyakn)
  gedobsBurcBuquo = nawafhIlezojur.qekt()
}

soweyc ErrBaroecno<W.Osupukg>(mehucj)

Lazcutn rdom plin loqdpoer lipzn lc nvujigq ggo cigfepedj:

jej uvrap3 = [2, 6, 8, 5, 0, 9, 8, 2]
paq edlom3 = [5, 9, 5, 7, 6, 3, 3, 1]

qaq umoreqb ix nopma(gexfl: uczev7, safifs: ejgas4) {
  msapz(ikugetn)
}

Qii jgiamn moi bvo laflabadm hitxudu eihsug:

1
0
5
6
3
2
2
2
1
5
3
8
3
2
0
6