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Solutions for assignment #4 - Quick Sort #36

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Solutions for assignment #4 - Quick Sort #36

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237 changes: 169 additions & 68 deletions ...nts/Sorting/QuickSort.playground/Pages/Quicksort In-place.xcplaygroundpage/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -11,26 +11,50 @@ 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
var j = low
var i = j - 1

while j < array.count - 1 {
if isOrderedBefore(array[j], pivot) {
i += 1

guard i != j else {
j += 1
continue
}

swap(&array[j], &array[i])
j += 1
} else {
j += 1
}
}

i += 1

if i == high {
return i
}

swap(&array[j], &array[i])
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 @@ -41,26 +65,74 @@ 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 {


guard array.count != 1 else {
return 0
}

guard array.count != 2 else {
switch isOrderedBefore(array[0], array[1]) {
case true:
return 0
case false:
swap(&array[0], &array[1])
return 1
}
}

if low == high { return low }

// Following Wikipedia's example implementation
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 }
}



return 0
}

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

var hoareArray1 = [2, 5, 4]
assert(hoarePartition(&hoareArray1, low: 0, high: hoareArray1.count-1, <) == 0)
assert(hoareArray1 == [2, 5, 4])

// This one doesn't work with Wikipedia's example implementation
//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 hoareArray3 = [1, 1, 1, 0]
assert(hoarePartition(&hoareArray3, low: 0, high: hoareArray3.count-1, <) == 1)
assert(hoareArray3 == [0, 1, 1, 1])

var hoareArray4 = [5]
assert(hoarePartition(&hoareArray4, low: 0, high: hoareArray4.count-1, <) == 0)
assert(hoareArray4 == [5])

var hoareArray5 = [5, 3]
assert(hoarePartition(&hoareArray5, low: 0, high: hoareArray5.count-1, <) == 1)
assert(hoareArray5 == [3, 5])

/*:
### 1.3. Sort
Expand All @@ -70,32 +142,41 @@ 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
}

var divider = hoarePartition(&array, low: low, high: high, isOrderedBefore)

quickSort(&array, low: low, high: divider, isOrderedBefore)
quickSort(&array, low: divider + 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 @@ -119,24 +200,44 @@ func dutchFlagPartition<T: Comparable>(inout array: [T], pivotIndex: Int, low: I
var equal = 0
var larger = high

// ...

// Implementing Wikipedia's pseudocode https://en.wikipedia.org/wiki/Dutch_national_flag_problem#Pseudocode
while equal <= larger {
if array[equal] < pivot {
// Making sure I'm not swapping the same index
if smaller != equal {
swap(&array[smaller], &array[equal])
}
smaller += 1
equal += 1
} else if array[equal] > pivot {
// Making sure I'm not swapping the same index
if larger != equal {
swap(&array[equal], &array[larger])
}
larger -= 1
} else {
equal += 1 }
}
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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Original file line number Diff line number Diff line change
Expand Up @@ -3,44 +3,44 @@
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Expand Down