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Assignment 4 (QuickSort) Solutions #35

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46 changes: 28 additions & 18 deletions ...s/Sorting/QuickSort.playground/Pages/Quicksort Functional.xcplaygroundpage/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -7,27 +7,37 @@ This is a rather inefficient but neat solution. Pick a pivot and remove it from
*/

func swiftyQuickSort<T>(var array: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
guard array.count > 1 else {
return array
}

guard array.count > 1 else {
return array
}

let pivot = array.removeLast()
let lowers = array.filter {
isOrderedBefore($0, pivot)
}
let greaters = array.filter {
isOrderedBefore(pivot, $0)
}
let pivotsCount = array.count - lowers.count - greaters.count + 1
let pivots = [T](count: pivotsCount, repeatedValue: pivot)

return swiftyQuickSort(lowers, isOrderedBefore) + pivots + swiftyQuickSort(greaters, isOrderedBefore)
}

//let array1 = [1]
//assert(swiftyQuickSort(array1, <) == [1])
//
//let array2 = [Int]()
//assert(swiftyQuickSort(array2, <) == [])
//
//let array3 = ["c", "d", "b", "a"]
//assert(swiftyQuickSort(array3, <) == ["a", "b", "c", "d"])
//
//let array4 = [3, 0, 2, 1, 2, -1]
//assert(swiftyQuickSort(array4, <) == [-1, 0, 1, 2, 2, 3])
//
//let array6 = [5, 1, 2, 3]
//assert(swiftyQuickSort(array6, >) == [5, 3, 2, 1])
let array1 = [1]
assert(swiftyQuickSort(array1, <) == [1])

let array2 = [Int]()
assert(swiftyQuickSort(array2, <) == [])

let array3 = ["c", "d", "b", "a"]
assert(swiftyQuickSort(array3, <) == ["a", "b", "c", "d"])

let array4 = [3, 0, 2, 1, 2, -1]
assert(swiftyQuickSort(array4, <) == [-1, 0, 1, 2, 2, 3])

let array6 = [5, 1, 2, 3]
assert(swiftyQuickSort(array6, >) == [5, 3, 2, 1])
/*:
[Table of Contents](Table%20of%20Contents) | [Previous](@previous) | [Next](@next)
*/
211 changes: 128 additions & 83 deletions ...nts/Sorting/QuickSort.playground/Pages/Quicksort In-place.xcplaygroundpage/Contents.swift
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Expand Up @@ -9,28 +9,37 @@ Implement [Lomuto's partition algorithm]( https://en.wikipedia.org/wiki/Quicksor
*/

func lomutoPartition<T>(inout array: [T], low: Int, high: Int, @noescape _ isOrderedBefore: (T, T) -> Bool) -> Int {
let pivot = array[high]

// ...

return 0
let pivot = array[high]
var i = low
for j in low..<high where isOrderedBefore(array[j], pivot) {
if i != j {
swap(&array[i], &array[j])
}
i += 1
}
if i != high {
swap(&array[i], &array[high])
}

return i
}

//var lomutoArray1 = [2, 1, 4]
//assert(lomutoPartition(&lomutoArray1, low: 0, high: lomutoArray1.count-1, <) == 2)
//assert(lomutoArray1 == [2, 1, 4])
//
//var lomutoArray2 = [2, 1, 0]
//assert(lomutoPartition(&lomutoArray2, low: 0, high: lomutoArray2.count-1, <) == 0)
//assert(lomutoArray2 == [0, 1, 2])
//
//var lomutoArray3 = [5, 6, 0, 2, 1, 7, 3]
//assert(lomutoPartition(&lomutoArray3, low: 0, high: lomutoArray3.count-1, <) == 3)
//assert(lomutoArray3 == [0, 2, 1, 3, 5, 7, 6])
//
//var lomutoArray4 = [1, 1, 1, 0]
//assert(lomutoPartition(&lomutoArray4, low: 0, high: lomutoArray4.count-1, <) == 0)
//assert(lomutoArray4 == [0, 1, 1, 1])

var lomutoArray1 = [2, 1, 4]
assert(lomutoPartition(&lomutoArray1, low: 0, high: lomutoArray1.count-1, <) == 2)
assert(lomutoArray1 == [2, 1, 4])

var lomutoArray2 = [2, 1, 0]
assert(lomutoPartition(&lomutoArray2, low: 0, high: lomutoArray2.count-1, <) == 0)
assert(lomutoArray2 == [0, 1, 2])

var lomutoArray3 = [5, 6, 0, 2, 1, 7, 3]
assert(lomutoPartition(&lomutoArray3, low: 0, high: lomutoArray3.count-1, <) == 3)
assert(lomutoArray3 == [0, 2, 1, 3, 5, 7, 6])

var lomutoArray4 = [1, 1, 1, 0]
assert(lomutoPartition(&lomutoArray4, low: 0, high: lomutoArray4.count-1, <) == 0)
assert(lomutoArray4 == [0, 1, 1, 1])



Expand All @@ -42,24 +51,42 @@ Implement [Hoare's partition algorithm]( https://en.wikipedia.org/wiki/Quicksort
*/

func hoarePartition<T>(inout array: [T], low: Int, high: Int, @noescape _ isOrderedBefore: (T, T) -> Bool) -> Int {
let pivot = array[low]

// ...

return 0
if low == high {
return low
}

let pivot = array[low]
var i = low - 1
var j = high + 1

while true {
repeat {
j -= 1
} while isOrderedBefore(pivot, array[j])

repeat {
i += 1
} while isOrderedBefore(array[i], pivot)

if i < j {
swap(&array[i], &array[j])
} else {
return j
}
}
}

//var hoareArray1 = [2, 5, 4]
//assert(hoarePartition(&hoareArray1, low: 0, high: hoareArray1.count-1, <) == 0)
//assert(hoareArray1 == [2, 5, 4])
//
//var hoareArray2 = [5, 6, 0, 2, 1, 7, 3]
//assert(hoarePartition(&hoareArray2, low: 0, high: hoareArray2.count-1, <) == 4)
//assert(hoareArray2 == [1, 3, 0, 2, 5, 7, 6])
//
//var hoareArray3 = [1, 1, 1, 0]
//assert(hoarePartition(&hoareArray3, low: 0, high: hoareArray3.count-1, <) == 1)
//assert(hoareArray3 == [0, 1, 1, 1])
var hoareArray1 = [2, 5, 4]
assert(hoarePartition(&hoareArray1, low: 0, high: hoareArray1.count-1, <) == 0)
assert(hoareArray1 == [2, 5, 4])

var hoareArray2 = [5, 6, 0, 2, 1, 7, 3]
assert(hoarePartition(&hoareArray2, low: 0, high: hoareArray2.count-1, <) == 3)
assert(hoareArray2 == [3, 1, 0, 2, 6, 7, 5])

var hoareArray3 = [1, 1, 1, 0]
assert(hoarePartition(&hoareArray3, low: 0, high: hoareArray3.count-1, <) == 1)
assert(hoareArray3 == [0, 1, 1, 1])


/*:
Expand All @@ -69,33 +96,36 @@ By using your `hoarePartition`, implement an in-place quicksort.
*/

func quickSort<T>(inout array: [T], low: Int, high: Int, @noescape _ isOrderedBefore: (T, T) -> Bool) {

// ...
guard low < high else { return }

let p = hoarePartition(&array, low: low, high: high, isOrderedBefore)
quickSort(&array, low: low, high: p, isOrderedBefore)
quickSort(&array, low: p+1, high: high, isOrderedBefore)
}

//var array1 = [1]
//quickSort(&array1, low: 0, high: array1.count - 1, <)
//assert(array1 == [1])
//
//var array2 = [Int]()
//quickSort(&array2, low: 0, high: array2.count - 1, <)
//assert(array2 == [])
//
//var array3 = [1, 2, 3]
//quickSort(&array3, low: 0, high: array3.count - 1, <)
//assert(array3 == [1, 2, 3])
//
//var array4 = [3, 0, 2, 1, 2, -1]
//quickSort(&array4, low: 0, high: array4.count - 1, <)
//assert(array4 == [-1, 0, 1, 2, 2, 3])
//
//var array5 = [1, 2, 3]
//quickSort(&array5, low: 0, high: array5.count - 1, >)
//assert(array5 == [3, 2, 1])
//
//var array6 = [5, 1, 2]
//quickSort(&array6, low: 0, high: array6.count - 1, <)
//assert(array6 == [1, 2, 5])
var array1 = [1]
quickSort(&array1, low: 0, high: array1.count - 1, <)
assert(array1 == [1])

var array2 = [Int]()
quickSort(&array2, low: 0, high: array2.count - 1, <)
assert(array2 == [])

var array3 = [1, 2, 3]
quickSort(&array3, low: 0, high: array3.count - 1, <)
assert(array3 == [1, 2, 3])

var array4 = [3, 0, 2, 1, 2, -1]
quickSort(&array4, low: 0, high: array4.count - 1, <)
assert(array4 == [-1, 0, 1, 2, 2, 3])

var array5 = [1, 2, 3]
quickSort(&array5, low: 0, high: array5.count - 1, >)
assert(array5 == [3, 2, 1])

var array6 = [5, 1, 2]
quickSort(&array6, low: 0, high: array6.count - 1, <)
assert(array6 == [1, 2, 5])


/*:
Expand All @@ -113,30 +143,45 @@ When the algorithm is running, there are 4 groups of elements. We need 3 indices
*/

func dutchFlagPartition<T: Comparable>(inout array: [T], pivotIndex: Int, low: Int, high: Int) -> (Int, Int) {
let pivot = array[pivotIndex]

var smaller = 0
var equal = 0
var larger = high

// ...

return (smaller, larger)
let pivot = array[pivotIndex]

var smaller = 0
var equal = 0
var larger = high

while equal <= larger {
if array[equal] < pivot {
if smaller != equal {
swap(&array[smaller], &array[equal])
}
smaller += 1
equal += 1
} else if array[equal] > pivot {
if equal != larger {
swap(&array[equal], &array[larger])
}
larger -= 1
} else {
equal += 1
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@diegopetrucci diegopetrucci Jan 6, 2016

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Did you notice the function running indefinitely here? I also implemented the wikipedia's pseudocode and smaller is always ++ while the function is not breaking/return the tuple.

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@matax87 matax87 Jan 6, 2016

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I don't. It completes the calls and pass the tests. Did you try my version?
Let me know @diegopetrucci

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@diegopetrucci diegopetrucci Jan 6, 2016

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You're right, I was incrementing smaller, not equal. My bad. Thanks for the help Matteo!

}
}

return (smaller, larger)
}

//var dutcharray = [5, 1, 2, 2, 4, 5]
//let lowAndHigh = dutchFlagPartition(&dutcharray, pivotIndex: 2, low: 0, high: dutcharray.count - 1)
//assert(lowAndHigh.0 == 1)
//assert(lowAndHigh.1 == 2)
//assert(dutcharray == [1 ,2 ,2, 4, 5, 5])
//
//
//var dutcharray2 = [5, 10, 5, 5, 2, 5]
//let lowAndHigh2 = dutchFlagPartition(&dutcharray2, pivotIndex: 0, low: 0, high: dutcharray2.count - 1)
//assert(lowAndHigh2.0 == 1)
//assert(lowAndHigh2.1 == 4)
//assert(dutcharray2 == [2, 5, 5, 5, 5, 10])
//
var dutcharray = [5, 1, 2, 2, 4, 5]
let lowAndHigh = dutchFlagPartition(&dutcharray, pivotIndex: 2, low: 0, high: dutcharray.count - 1)
assert(lowAndHigh.0 == 1)
assert(lowAndHigh.1 == 2)
assert(dutcharray == [1 ,2 ,2, 4, 5, 5])


var dutcharray2 = [5, 10, 5, 5, 2, 5]
let lowAndHigh2 = dutchFlagPartition(&dutcharray2, pivotIndex: 0, low: 0, high: dutcharray2.count - 1)
assert(lowAndHigh2.0 == 1)
assert(lowAndHigh2.1 == 4)
assert(dutcharray2 == [2, 5, 5, 5, 5, 10])


/*:
### 1.5. Reading Swift Source Code
Expand Down
16 changes: 8 additions & 8 deletions ...orting/QuickSort.playground/Pages/Quicksort In-place.xcplaygroundpage/timeline.xctimeline
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Expand Up @@ -3,44 +3,44 @@
version = "3.0">
<TimelineItems>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1602&amp;EndingColumnNumber=10&amp;EndingLineNumber=34&amp;StartingColumnNumber=9&amp;StartingLineNumber=34&amp;Timestamp=472497062.906165"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2065&amp;EndingColumnNumber=10&amp;EndingLineNumber=61&amp;StartingColumnNumber=9&amp;StartingLineNumber=61&amp;Timestamp=473006475.246227"
selectedRepresentationIndex = "2"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1602&amp;EndingColumnNumber=10&amp;EndingLineNumber=34&amp;StartingColumnNumber=9&amp;StartingLineNumber=34&amp;Timestamp=472497062.906439"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2065&amp;EndingColumnNumber=10&amp;EndingLineNumber=61&amp;StartingColumnNumber=9&amp;StartingLineNumber=61&amp;Timestamp=473006475.246504"
selectedRepresentationIndex = "2"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1602&amp;EndingColumnNumber=14&amp;EndingLineNumber=34&amp;StartingColumnNumber=13&amp;StartingLineNumber=34&amp;Timestamp=472497062.90666"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2065&amp;EndingColumnNumber=14&amp;EndingLineNumber=61&amp;StartingColumnNumber=13&amp;StartingLineNumber=61&amp;Timestamp=473006475.246735"
selectedRepresentationIndex = "0"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1617&amp;EndingColumnNumber=14&amp;EndingLineNumber=68&amp;StartingColumnNumber=9&amp;StartingLineNumber=68&amp;Timestamp=472497062.906874"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2253&amp;EndingColumnNumber=14&amp;EndingLineNumber=98&amp;StartingColumnNumber=9&amp;StartingLineNumber=98&amp;Timestamp=473006475.246963"
lockedSize = "{179, 289}"
selectedRepresentationIndex = "1"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2287&amp;EndingColumnNumber=14&amp;EndingLineNumber=69&amp;StartingColumnNumber=9&amp;StartingLineNumber=69&amp;Timestamp=472497131.944604"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=2886&amp;EndingColumnNumber=14&amp;EndingLineNumber=99&amp;StartingColumnNumber=9&amp;StartingLineNumber=99&amp;Timestamp=473006475.247198"
lockedSize = "{178, 287}"
selectedRepresentationIndex = "1"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1014&amp;EndingColumnNumber=10&amp;EndingLineNumber=37&amp;StartingColumnNumber=9&amp;StartingLineNumber=37&amp;Timestamp=472497062.907309"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1463&amp;EndingColumnNumber=10&amp;EndingLineNumber=64&amp;StartingColumnNumber=9&amp;StartingLineNumber=64&amp;Timestamp=473006241.853156"
selectedRepresentationIndex = "2"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1458&amp;EndingColumnNumber=10&amp;EndingLineNumber=38&amp;StartingColumnNumber=9&amp;StartingLineNumber=38&amp;Timestamp=472497062.907522"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1894&amp;EndingColumnNumber=10&amp;EndingLineNumber=65&amp;StartingColumnNumber=9&amp;StartingLineNumber=65&amp;Timestamp=473006475.247656"
selectedRepresentationIndex = "2"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
<LoggerValueHistoryTimelineItem
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1014&amp;EndingColumnNumber=10&amp;EndingLineNumber=34&amp;StartingColumnNumber=9&amp;StartingLineNumber=34&amp;Timestamp=472497062.907733"
documentLocation = "#CharacterRangeLen=0&amp;CharacterRangeLoc=1463&amp;EndingColumnNumber=10&amp;EndingLineNumber=61&amp;StartingColumnNumber=9&amp;StartingLineNumber=61&amp;Timestamp=473006241.853604"
selectedRepresentationIndex = "2"
shouldTrackSuperviewWidth = "NO">
</LoggerValueHistoryTimelineItem>
Expand Down
1 change: 1 addition & 0 deletions ...ents/Sorting/QuickSort.playground/Pages/Table of Contents.xcplaygroundpage/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -9,3 +9,4 @@
****
[Start](@next)
*/