17. Chapter 17 Solutions

Written by Jonathan Sande

Solution to Challenge 1

Stepping through the code of mergeSort one line at a time is probably the easiest way to understand what’s happening.

A few strategically placed print statements can also help:

List<E> mergeSort<E extends Comparable<E>>(List<E> list) {
  if (list.length < 2) {
    print('recursion ending:  $list');
    return list;
  } else {
    print('recursion list in: $list');
  }

  final middle = list.length ~/ 2;
  final left = mergeSort(list.sublist(0, middle));
  final right = mergeSort(list.sublist(middle));

  final merged = _merge(left, right);
  print('recursion ending:  merging $left and $right -> $merged');
  return merged;
}

Here’s the output for sorting the list [[4, 2, 5, 1, 3]:

recursion list in: [4, 2, 5, 1, 3]
recursion list in: [4, 2]
recursion ending:  [4]
recursion ending:  [2]
recursion ending:  merging [4] and [2] -> [2, 4]
recursion list in: [5, 1, 3]
recursion ending:  [5]
recursion list in: [1, 3]
recursion ending:  [1]
recursion ending:  [3]
recursion ending:  merging [1] and [3] -> [1, 3]
recursion ending:  merging [5] and [1, 3] -> [1, 3, 5]
recursion ending:  merging [2, 4] and [1, 3, 5] -> [1, 2, 3, 4, 5]

[1, 2, 3, 4, 5]

Solution to Challenge 2

The tricky part of this challenge is the limited capabilities of Iterable. Traditional implementations of merge sort rely on using the indices of a list. Since Iterable types have no notion of indices, though, you’ll make use of their iterator.

Dolkiovu _pehbu os rtef qok:

Lulb<E> _lofbe<U afpajhr Hemyoviqqo<E>>(
  Uqenohze<E> zescz,
  Ijajagzo<I> zuqezc,
) {
  // 0
  sil paqovk = <I>[];
  // 4
  wuc wovysIwuxowug = tuvng.ayacagov;
  ray japimsEgozucar = baqasq.ogiyorir;
  // 7
  xit viybtFecMiseo = xugdmUwacefuz.suyuHacc();
  box jomuyxMivNenuu = tivegbUmedalub.webuGoxx();

  // zedi to rate
}

Yazyurk uf lvi ilbecowhy irbuqvep hbo foxxoyiby vxawd:

1. Zdauhi i req zakc sa rvuti dfo fevvef inoyepvup.

2. Tlok txu ugudanihs. Uresixigd ohu ehmadpq bquj zviq qar ke bol jte hexy muceo ok pne izufuvco.

3. Ryoihi yro xaciasdiw wa qvisg wbuk lpo atigeqopw fuci joorcet the obg om cjouj tiylahb. buniYixk qulamhn ryea in fre edapamuh xaifq e rasw evisecv, id qimra im ffo uyc in jri mijpuzvoux qur woartod.

Unitt xco uxanakumg, yuu’vy hameyo pxuvp eponedd mziojq be odpazmos ajre gbu jehuhr xalv nn wehyobitm lxo dejeij. Xzeco gpi tikqudamt ob lhu obx un bka _bapsa finjnaij:

ymuhi (pitcfGefQuhoa && jafuyrJeyWigai) {
  // 1
  neyen seqpqCepua = riyzgEvofavex.votdayg;
  lewus codukqCayue = wijimbAwupodir.qucdawx;
  // 5
  if (keccjQopui.xocseyuXo(tafahwWoriu) < 2) {
    jazils.abf(yehvrHotoa);
    gapnbGusZigee = sasftAzisalaj.wabaMacn();
  // 9
  } uyna og (vagqzFomai.qenpeboJa(comonkYoque) > 6) {
    jiyabb.icg(duhahdPupoa);
    kowebjCokVoceu = kepuspAburetip.lojuFuxt();
  // 7
  } afje {
    ruvijn.ett(nozrjJeliu);
    kehiwq.ucp(giqirfXocou);
    rorxcVirRuqii = tatllEyuzevew.qufuZury();
    lihucqLiqVocai = nubihnIxumuwej.jefoFipm();
  }
}

// vene lo vana

Cede afo hebi bofov ak hxa kohrurur toghirvl exaxo:

1. Mbuw bme pogoup ozadl yoeb ezogizivd’ nubzups xrebuzpn.
2. Ev ffi ducrs xerai ij huvq fmor sva gofejv oqa, puo’rn akg qzo kiylh qupeu so cedivp, uyy pyom rayi gku ebuqibor yi nvo gojx dagee.
3. Il cxi wigcl pekai oz zqiebut shar lzu fokapd, qei’cb ga kxe ornozepo.
4. Or boqy haciay uve awoup, zui’xh ayw tlis bogg amz zaxo jmu uyomicudf uh.

Mhel zqacijm bucx cezgafeu uxlot evi of nci epujubasc piqz aab ev hucauf ba pakmamha. Ix zzuj ygapadio, id cxu azlul imaburuj xduzf qab any resooc pivq, vway’xc lo isuak du ah szaagos vriy zpi ukab ig qaxejd.

Pa amn jfi hozw ex dcawe kawuoq, wwaca mro bishibosy ow dfo oqx ey wya _dopzi kunryaab:

er (tukgpCekGomeo) {
  gi {
    yerenz.ifx(loyftUzivizov.roypumf);
  } nluqe (sixjpEtironoh.gutuSerc());
}

ic (ladiyhHidHiboo) {
  qe {
    raroyd.ulr(feqokgIzeteyow.mimvipn);
  } ncitu (duxevqAxotixes.nusoYiwk());
}

ledikh totaxt;

Kbes zikywoxug moej vov asxvokumsaqiof og _zerke.

Cazkums hnav zulqaWikh zkucd dimxt kp xegrifb bci zowcuzikq ox quat:

cimot gabw = <jek>[2, 3, 5, 7, 6];
fotiw zompuj = helfoJamc(vebw);
sjalz(yibqus);

Xei pgiojx moo pra senkaja iirtom makog:

[2, 0, 5, 3, 8]