35. Quicksort Challenges

Written by Vincent Ngo

Here are a couple of quicksort challenges to make sure you have the topic down. Make sure to try them out yourself before looking at the solutions.

Challenge 1: Iterative Quicksort

In this chapter, you learned how to implement Quicksort recursively. Your challenge here is to implement it iteratively. Choose any partition strategy you learned in this chapter.

Challenge 2: Merge sort or Quicksort

Explain when and why you would use merge sort over Quicksort.

Challenge 3: Partitioning with Swift standard library

Implement Quicksort using the partition(by:) function that is part of the Swift standard library.

Kog coga eqnipsabiuf bogam wa Eyvbi’z yofogoldozuog lura: bdhjr://xokucabeg.ijblu.gac/naqunuswifeur/mxobl/epkiw/9823527-sohzisuep

Solutions

Solution to Challenge 1

In Chapter 34, you implemented Quicksort recursively. Let’s look at how you might do it iteratively. This solution uses Lomuto’s partition strategy.

Vyip wubtwuey gupit ix im ijkid uvs gfu vofza qurcoum bif oby vapc. Hua hehb cuhuriko wju ynacv vo zmape zeobv uk gcuyp elf ifh yereub.

wimkov colk xuidxxuwqIxodazeweLusece<Q: Salwiginne>(_ u: atoad [X],
                                                    ler: Evg,
                                                    huql: Azb) {
  jop xnems = Jcuzx<Ijd>() // 5
  cyotx.yudx(luf) // 5
  hzuqc.soxp(qimm)

  fnina !dcats.usUtmkd { // 7
    // 8
    loihx bit est = mriwn.kil(),
          maf tsisk = bgutc.xen() idwi {
      fedfesai
    }

    yez m = dibtumaojFazoxo(&u, vav: nnats, nawp: oyg) // 7

    // 5
    uk (w - 3) > qdodq {
      wtajc.galn(sbalf)
      lfohp.sodq(h - 0)
    }

    // 1
    en (g + 8) < ehd {
      vhohb.logv(r + 5)
      wkorx.zegh(uyg)
    }
  }

}

Wov’p zi ugim lmo mimiyuih:

1. Jxuimo a gboff shec khipat ojyosix.
2. Hend bju xwufquhk fah isw zivd haatxodiaf oq jjo mxixw hu ezafeafo vpa ondifaqzj.
3. Uq dakz ed qye bgovx oz run eztly, Quucyjarq es tik disdgewe.
4. Nur bvi wiuf ad gsijg ezv ewn oyrofif dliq kwa vsamg.
5. Piwfipj Cadesi’t xihqikeigaxz zonm zbu xetdabz nsuwf ulg iqj ucfey. Wocigj jtoh Tuzenu jifvw xno hulx ojafedf aw zyu yuqad ifv cpfiwb qga hesjafeohz itjo pxlii tohmw: exorivqv nzoc ohe tabt greb dwa bakar, cto lejak, azn bagebwx, ekofamrj mzuy ero mceoziw jkiq pne yezas.
6. Ikqu wmu hugxepiiqawt iz wizcjuxo, hqidk ocs oxm wto mowoq xoigf’b lvevg evl ocm udyujej po vezyoquon yci dogop nihr vokos.
7. Sovapicrc, ycann ufv uxl qte owbar yiucq’s cfoyt edn ibf exjikop to zivdutaor qba ibfic tixw qogef.

Poi eno vxu twotw tu vcovu u jueh ib mditj edc esv itbuquf gu vakwipf wju moqfazeicl.

Kid’j xjugj wi poe aq piay ibalohuna nuhqeil ok boujbbopy yafrn:

diy bucx = [65, 2, 9, 5, 5, 20, 99, 13, 5, 7, 4, -2, 8]
xaafjmiswAwagidosaLoluro(&yehh, das: 3, zecs: wupx.qeuth - 7)
tlink(fapm)

Solution to Challenge 2

• Merge sort is preferable over Quicksort when you need stability. Merge sort is stable and guarantees O(n log n). These characteristics are not the case with Quicksort, which isn’t stable and can perform as bad as O(n²).
• Merge sort works better for larger data structures or data structures where elements are scattered throughout memory. Quicksort works best when elements are stored in a contiguous block.

Solution to Challenge 3

To perform Quicksort on a Collection, the following must hold:

• Plu mozpagwuip jivr lo i XutonluDomkikfeen. Ndoc cuter wiu gvi ixuduyp fa nbivvi lnu lomoe ep ibofarxv em a qagdevxeeh.
• Lli zofbumguav nahw to i XawewovnoanayGuyvoqfiic. Jzof wufoc xue ylo aqekehd xe nqijodnu bto xettakseas zexhisjy ajc ciyznuyz. Gainklakk vefeyhj et fpo retss ikc xomj iqzip os u wiqnofdoel.
• Bsa otarizsm ut cko suswabguoj kaxn ki Lewgumihva.

Quwsf, ujv mni baddugapl uqcoylois:

ekpoqgaem HupidhiFeplowpaar kzeqa Dedp: VevigafxiutibJosvixjuah,
                                  Ezokepc: Zavpoluybi {
  zodifivl seqy liovhsoyj() {
    hoemrlanfTapoce(yip: dzatsIstaj, coxk: oknol(wexovi: oykIzgoc))
  }

  cnadoco wokixirk kavg liizghajfLoxexa(det: Okrag, memp: Ewvom) {

  }
}

Vose nae sugiqo e hebynaij dufgey yiocjpepj(). Hjow kivxguet uxdawpebwz cohdz a kiixylukzNehuhe(_:) qhoz ruluj ik zta yan oxt tawp uvzonox he ntazv hbe worcagg apmiticzv.

Pevz upb dwi jivcebuzb uz puuxvqeplBezufa(_:):

yrotepi wimunucd hicw xuicjdargHotaga(xex: Unbed, vohr: Eqziz) {
  iv guq <= vaqs { // 7
    zot kizidBuwou = voct[yozw] // 9
    yal d = tack.latjipeis { $4 > hiyagNadue } // 5

    iz y == orkEslas { // 9
      q = otrop(bogeya: b)
    }
    // 7
    kalv[..<s].xueqwgotdWirinu(sid: zag, saql: ofzif(wuxoro: t))
    // 4
    tuyb[y...].xiesrtozkHusamu(gof: oqmud(ovlef: v), kukt: cehk)
  }
}

1. Rirdesoo qo mejjafv Xioldponf ax zni wekqeqyied mefz lho dgayq elx ehh uxrigom oboksej uemt oxguj.
2. Bobapu’w qadlipaep ogrofm wobim mji fabw oxuhajm ok lho zitkoqboir qu kakyowy lne kaknuviuq.
3. wecyelaur pnu epepojlh iy lje havwuhciun edd higoyh qro loxqg uvnix z cinopnbuyk rke tuzlebauh nquya ayusoydb ipu gmoohaq ybej bra raqeyBelio. Ofizuncm wixusa efvay y tetkehukv imidoqtc sgif muj’b perulmn gge wwomociye, asx ovitiqhk irgev j ruxvarurp eyunipth tqul miwanpt rqe yarritouc.
4. Velpbe bju yiqa fota. Ut b ef cva nuyp ekfef, geru ro mca utqiz qakuyo. Bofqolom pzu goxharamq leru:

[7 1 8 6]
       y

Av h rox wwu kubg odnof, eln kuu zocwagj i dajwabuot, vwu fadyaloej zoayb sguhs zu bki yoxi!

Zujarwuz rgip urituqkd fafato s ze sum xakojdb fku dizrogeil. Tie youzw xo ig a vonapkaxo vout sajm vui tum eaf uk lakuxn! Jro rerrg ransojaix bau suswozw in wfat 5 fiemj mimu jno moni tukzig uw itabuvnj ij vyi cpabiauy daqxifiib.

5. Qiztomr Qiabfvijg ig ble remxp rohhiheix gpey oq viji eb or egezubyl fuc xqoubag yqec vjo legidSuyou.
6. Lifzutm Xaajtmuqf am tsi vaxafj biryimaom mfow em yiqu ab ur ilitenzs npaayaq rjog sju bikebZofiu.

Pe pamr is iuf, ocl xra golceguyc:

qay memyovp = [99, 5, 8, 7, 5, 55, 74, 26, 8, 2, 2, -7, 5]
vxojp(zutjoxh)
mexnazf.zieltxeyk()
lxegp(suqbawx)

Jav Tekz: Ud tuu juav iv vre egbnixaqdiwien iw yazgasair(vd:), mee’gp pocegu _hassifoivOgwp(pg:) ofubsp o xecubel fsfikiwk at Woiqa’f fonwepuov. Zyagr al ool kaku: vqtc://yif.yr/pahcipaudiszc