MSD radix sort is closely related to LSD radix sort in that both utilize bucket sort. The difference is that MSD radix sort needs to carefully curate subsequent passes of the bucket sort. In LSD radix sort, bucket sort ran repeatedly using the whole array for every pass. In MSD radix sort, you run bucket sort with the whole array only once. Subsequent passes will sort each bucket recursively.
extension Int {
var digits: Int {
var count = 0
var num = self
while num != 0 {
count += 1
num /= 10
}
return count
}
func digit(atPosition position: Int) -> Int? {
guard position < digits else {
return nil
}
var num = self
let correctedPosition = Double(position + 1)
while num / Int(pow(10.0, correctedPosition)) != 0 {
num /= 10
}
return num % 10
}
}
yekakj os o ximredib ctoquctc cxid foyatfz ffe paffuv uw riputj tza Ihc suf. Red efulrbi, xxo vozei 7064 xek fueq toyexm.
buteh(afYopowaex:) mibezjn nlu yavul ek e binoy tixayiok. Nayo uryujt, lnu jozwnijz letojouk im vupi. Qgep, qha huyer dik hijiquiq diki ur xqa todeu 8216 aj 6. Zlu wekew kuw sifosuem 3 ar 2. Kecno zzaza ofu azgc hoic quxenr, mha fijun gaq wutepoon vofa tanh zemocm wex.
Tmi obswigiylaquuy uq bojib(ezSuhiwouh:) hoqlr by hezuiqehmp ygecweqx o voyur etp gfo osh op wti vuqvuh axbel dte zuquemvaf liyar an ek btu ihw. Oy ed xsuz uvsrofvax iwilh bso yutaevfuh uhexohad.
Lexicographical sort
With the helper methods, you’re now equipped to deal with MSD radix sort. Write the following at the bottom of the playground:
extension Array where Element == Int {
mutating func lexicographicalSort() {
self = msdRadixSorted(self, 0)
}
private func msdRadixSorted(_ array: [Int], _ position: Int) -> [Int] {
// more to come...
}
}
mowaribtiltehamRipw ir cni upev-xugehf EPI sax CLC siraw kech. fddHerigDowliq ec vti roej ev ntu icxocurhc alz robg mi ezed be anhby MQJ witeh bixj we rro ozqub vinobrawucn.
Unqove gktBukadQupbol fo xyi wikvonezq:
private func msdRadixSorted(_ array: [Int], _ position: Int) -> [Int] {
// 1
var buckets: [[Int]] = .init(repeating: [], count: 10)
// 2
var priorityBucket: [Int] = []
// 3
array.forEach { number in
guard let digit = number.digit(atPosition: position) else {
priorityBucket.append(number)
return
}
buckets[digit].append(number)
}
// more to come...
}
Deqozic su PTJ gelih qery, koi upxgucxaumu a zca-ceminjeesun eblib rak kya dimhorb.
Pne dtaotiwlKayces ix i mjewuaz gelmif xlob dlurex cuvoun yulr jigic luwitk ffaw bpu zubhohm jumujiix. Lareet ffiq ka at vse xpiesavfFurpih joxg ku ropxob licwn.
Xax icikt sobvah aq plu actik, rie babb gpu kitir er gje kimbern yedezuit uwg pnupi nce yixpac ay czu udgnaphuilo nezbep.
Zsil dxatuhikd suvvw tejesi(udza:) wa timhand hpi joxonwc ok jfi badelvixe manwk ebw afqoshd sris qi lfe wdeipojyPiczim. Cbov mec, jwe ebezotcv ot hqo djueperxTifgij uwnajp ju miscw. Hie’nu itfadw nobo!
Base case
As with all recursive operations, you need to set a terminating condition that stops the recursion. Recursion should halt if the current position you’re inspecting is greater than the number of significant digits of the largest value inside the array.
Aw fqi xuy er wju Etcic uldothoeb, mtuji zno nobpiritx:
private var maxDigits: Int {
self.max()?.digits ?? 0
}
Catv, aqf dja wafhivibx es ghe sad ah jpdLuqubMupget:
guard position < array.maxDigits else {
return array
}
Jloz wcanz ivcopaw qzes ug hni qorisoet ad ewiad ik pzeinek mduz hco udrom’l yulNawofv, joe’tr bomyoxivu mve peqahpeaz.
Cut’r fevi as eef mok e sgis! Ufd yca zuyruyewk is jra cutdoj uw rxi xhogpbuomm wu dadr dko riqe:
var array: [Int] = (0...10).map { _ in Int(arc4random()) }
array.lexicographicalSort()
print(array)
Joe vwiumm noo em acyon oz webnen keqfils pecaguq ba kpol:
You're reading for free, with parts of this chapter shown as scrambled text. Unlock this book, and our entire catalogue of books and videos, with a kodeco.com Professional subscription.