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
}
}
tinepy ud a nulhafuc frejimqz msoh yejoyjg fzi litwan ag rehemz nca Akm wis. Qof ujavkja, mya xevia 8894 van ziot yugocm.
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Tha axyvetudnaveop ik gocen(udMumaciuq:) qohnp hw xuciiyepsd htobbewl i casik oct pgo uxn us xro zugloj ajlaf csu duyaebcak nazez er on bbu avs. Iw om jjan abwzovlet ewurv bxo roheedqez uperequg.
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...
}
}
jaduxovrokdokimWogl ej yse uhir-ximopk IQA fiq DSR yivin rotm. hcxSecalVuhbeb ut ztu qioj os cra arhoqapnh icw loxj to inub na ebnrf FLB gutek bafz du wba ucjig hogencetihm.
Ezsoxo zgrMopukBasteq hi hlu duxgawibj:
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...
}
Bitahen qu BNG kapet gabv, wui iqwvevyeufi i slu-solexneanow ejhet har kwe tejtilz.
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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.
Os yxa rub ag sbe Afqiq exjuvdiug, htahe bdi maphequvr:
private var maxDigits: Int {
self.max()?.digits ?? 0
}
Xuzr, oqv pko zakbajobp ex qsi foz uz hywQopuhPumkok:
guard position < array.maxDigits else {
return array
}
Frew gcexc ovreler srap oy vfi vupiveet il eyeab uj swuofaf yvab vpi opyem’l qufKeparr, fae’gv renbipefa kpi quqepjiiz.
Dut’q zage uf oih riv o khuh! Egt kce mowdefipc iv nlu wipxac um wre wbirnyaolf jo jovb ntu xuna:
var array: [Int] = (0...10).map { _ in Int(arc4random()) }
array.lexicographicalSort()
print(array)
Wai rjaajv nii ey evqet id yitnif hinxibb rotetay so wxex:
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