Quicksort in Swift

gistfile1.swift

var randomNumbers = [42, 12, 88, 62, 63, 56, 1, 77, 88, 97, 97, 20, 45, 91, 62, 2, 15, 31, 59, 5]

func partition(v: Int[], left: Int, right: Int) -> Int {
    var i = left
    for j in (left + 1)..(right + 1) {
        if v[j] < v[left] {
            i += 1
            (v[i], v[j]) = (v[j], v[i])
        }
    }
    (v[i], v[left]) = (v[left], v[i])
    return i
}

func quicksort(v: Int[], left: Int, right: Int) {
    if right > left {
        let pivotIndex = partition(v, left, right)
        quicksort(v, left, pivotIndex - 1)
        quicksort(v, pivotIndex + 1, right)
    }
}

quicksort(randomNumbers, 0, randomNumbers.count-1)

This is your solution with a bit modification for Swift 5:

var randomNumbers = [42, 12, 88, 62, 63, 56, 1, 77, 88, 97, 97, 20, 45, 91, 62, 2, 15, 31, 59, 5]

// MARK: - Solution 1 : Naive
func quicksort1<T: Comparable>(_ list: [T]) -> [T] {
	if list.count <= 1 {
		return list
	}

	let pivot = list.randomElement() ?? list[0]

	var smallerList = [T]()
	var equalList = [T]()
	var biggerList = [T]()

	for x in list {
		switch x {
			case let x where x < pivot:
				smallerList.append(x)
			case let x where x == pivot:
				equalList.append(x)
			case let x where x > pivot:
				biggerList.append(x)
			default:
				break
		}
	}

	return quicksort1(smallerList) + equalList + quicksort1(biggerList)
}
quicksort1(randomNumbers)

// solution 1 with array extension
extension Array where Element: Comparable {
	func quicksort1() -> [Element] {
		let list = self
		if list.count <= 1 {
			return list
		}

		let pivot = list.randomElement() ?? list[0]

		var smallerList = [Element]()
		var equalList = [Element]()
		var biggerList = [Element]()

		for x in list {
			switch x {
				case let x where x < pivot:
					smallerList.append(x)
				case let x where x == pivot:
					equalList.append(x)
				case let x where x > pivot:
					biggerList.append(x)
				default:
					break
			}
		}

		return smallerList.quicksort1() + equalList + biggerList.quicksort1()
	}
}
randomNumbers.quicksort1()