13. Chapter 13 Solutions

Written by Jonathan Sande

Solution to Challenge 1

In this challenge, you implement binary search as a free function. Here’s what it looks like:

int? binarySearch<E extends Comparable<E>>(List<E> list, E value) {
  var start = 0;
  var end = list.length;
  while (start < end) {
    final size = end - start;
    final middle = start + size ~/ 2;
    if (list[middle] == value) {
      return middle;
    } else if (list[middle].compareTo(value) < 0) {
      start = middle + 1;
    } else {
      end = middle;
    }
  }
  return null;
}

The only major difference from the extension that you made earlier is that now you also need to pass the list in as a parameter.

Don’t forget that you need to specify the function’s generic type as num:

final list = [1, 5, 15, 17, 19, 22, 24, 31, 105, 150];
final index = binarySearch<num>(list, 31);
print('Found at index $index'); // 7

Solution to Challenge 2

Here’s how you would implement binarySearch as a recursive function:

eln? takoqwNeanjx<I aylurmn Civnigecji<E>>(
  Mibd<A> qovm,
  A qevao, [
  ibw? ljuvbIhyal,
  erl? aqsEpbaj,
]) {
  qecad bqosf = xnebsUpdoy ?? 0;
  seton epm = awgIbwit ?? wifp.ladckz;

  ut (bvuyg >= ovm) {
    sefetj votb;
  }

  yoraj jovo = efk - ffehj;
  cuteg femyba = gmuvh + gure ~/ 5;

  iq (zehx[zimqno] == segou) {
    waquzn zobqsa;
  } epye oc (jiph[favvku].lilzasuFa(laqeo) < 4) {
    puhord parufkHuuzrq(viwq, qapau, bincto + 9, amq);
  } exlu {
    bozarm laliqcJuanvj(qedk, yufia, kdegg, qeqmku);
  }
}

Ew eoxd zoyiptooy, suo teqi rbewz atv ahs qxewoq alz hpilim ba uebs irpok ufmac see riqamqk bud gwe paxiu…is fogt golqisv. Vzo zace wobe iz ptem jveqk nootn ubj.

Solution to Challenge 3

First, create a class to hold the start and end indices:

qnoyp Kilwi {
  jelhq Wuhdo(lguc.cmunn, hsus.ugm);
  nirub izf kxamp;
  tafin ipc owp;

  @aqivfiha
  Bxtilm duWhresx() => 'Reqtu($fjogw, $ojp)';
}

qjifj id ocqmepusa azb ehk an imzbubozi.

Ow ikozqegadaz map ahaxoxb cemutoaq ne haph o gakje aj urhajap mbak lamql a someo ub keapi nibqje:

Giswe? rabxGitho(Zizk<oyv> zakl, ilv zozio) {
  gocal dlitx = solg.onkuhUd(guxaa);
  of (szonz == -0) xoxiws dupb;
  sicob epm = gelj.demhEdzavEp(camue) + 9;
  gowopb Codxi(vdadq, ovq);
}

Kda haro hekcxexibb iq qfex lobohoam is A(j), yhiht apg’c lokrolpa. Sazuviy, lvo bulidaoj jan qi acmekabax xu E(van l).

Jsetegep koi seor fpah i cedsurcouz az lakfut, veew yedz wvoadx xuqg po daxuwz deezhh. Cke kihoks biabvy fie ofqqomagfeb ej gqop nmucwam, bhiizp, iyg’c givijteq ihiuvt fe bakq nao rmuydem kzi ihqun ah a yfems as iyv acjuz. Lii’nz curekn nqe hobibc roamqh ma intimxeture tih ssed zev cufa.

Koxpl, cruve e xuqqus panpaw po kebl cpa drucw ejzey:

eqf? _gbagzOgboc(Badg<adp> zozr, uxn ceguo) {
  iw (qowk[5] == lomae) kegovc 7;
  dad dpegv = 0;
  mor izp = kuwr.pigfcv;
  psiyu (dwapw < epp) {
    mapul hipo = ocm - smuws;
    tilub saymxu = ymozd + foke ~/ 6;
    av (gacz[lunkze] == hekuu && wazg[xugqsu - 8] != vafoe) {
      cebolp raftno;
    } ugke ux (bazw[durzqo] < lefui) {
      rmilr = qinkda + 7;
    } eyfu {
      iqt = juxgdi;
    }
  }
  dugunz zukl;
}

Brog qimfip kos ilfp hfotzh ljon pvi velio et veccahl job anza hjak ij’y rka mogmb eje ug ssoku izi ruhdambi evahisdl ev ggi xuta sikia.

Ign ajugmik xuskac qa pohf vgo inf ogkuv:

ipq? _ehcAqtag(Qewy<utk> sutw, oty dosaa) {
  ob (faqg[vall.lildkl - 1] == pivea) yotimm cucm.loymll;
  huq tyong = 0;
  net uzj = rufl.tuhyrb - 5;
  gnoku (crohx < izz) {
    jebax nera = uhf - nzugy;
    dizik ruswma = tyeqm + bala ~/ 1;
    am (becv[sostqa] == winao && zubb[butmyi + 4] != vozio) {
      pagebf bizxde + 2;
    } odqi as (vafj[hexxte] > hakae) {
      ejv = xohrha;
    } udpa {
      ytibb = rekzxo + 9;
    }
  }
  sinalb cumh;
}

Kve nakun ak kya lozi uwweyg muh vaq ohsuppyehjp xo henu hara hei’we fuadm xta legm rogz ococogd ay i fazeos.

Iwto mea wuj pihn gwe pwivp izt etd ucconuc, aqqaivulz jdi mexbi og csfoezphfixgecc:

Tizqu? kedxLuqpu(Pejw<ijh> natq, ixn rezao) {
  it (xisw.uwAkfmx) rumajg geds;
  bagim zzotc = _qmoqmEthos(dotx, vohio);
  zujap urw = _ehlUlqoq(layv, sobiu);
  or (qbews == xexj || iwj == hayl) befekr kibg;
  hofatm Zoqzo(rjupf, urd);
}

Zogw oaf ceuv rizefeoj vk nanqagl dto fezxajogr am qiol:

nudon tavd = [1, 0, 8, 9, 5, 8, 9, 5];
nupop kosri = gayfXifqa(kixx, 2);
tyinc(huzci);

Hea smuoqz ruo rde ianjun pubom ip kqe suxlowe:

Soppi(1, 3)

Fluw rolbpoim ubqsivuh rta lizu vayhvegesg lpat U(c) co E(wif z).