Quick Sort in Swift

Quick Sort

in Swift

Welcome to the Quick Sort in Swift page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

import Foundation

let usage = """
    Usage: please provide a list of at least two integers to sort in the format "1, 2, 3, 4, 5"
    """

extension StringProtocol {
    var trimmed: String { trimmingCharacters(in: .whitespacesAndNewlines) }
}

func parseIntegers(from args: [String]) -> [Int]? {
    guard args.count == 2 else { return nil }

    let parts = args[1].split(separator: ",", omittingEmptySubsequences: false)
    let values = parts.compactMap { Int($0.trimmed) }

    guard values.count == parts.count,
        values.count >= 2
    else {
        return nil
    }

    return values
}

extension RangeReplaceableCollection
where Self: MutableCollection, Self: RandomAccessCollection {

    mutating func quickSort(by areInIncreasingOrder: (Element, Element) -> Bool) {
        guard count > 1 else { return }

        var buffer = Array(self)
        quickSort(&buffer, low: 0, high: buffer.count - 1, by: areInIncreasingOrder)
        self = Self(buffer)
    }

    private func quickSort(
        _ a: inout [Element],
        low: Int,
        high: Int,
        by areInIncreasingOrder: (Element, Element) -> Bool
    ) {
        guard low < high else { return }

        let pivotIndex = partition(&a, low: low, high: high, by: areInIncreasingOrder)

        quickSort(&a, low: low, high: pivotIndex - 1, by: areInIncreasingOrder)
        quickSort(&a, low: pivotIndex + 1, high: high, by: areInIncreasingOrder)
    }

    private func partition(
        _ a: inout [Element],
        low: Int,
        high: Int,
        by areInIncreasingOrder: (Element, Element) -> Bool
    ) -> Int {
        let pivot = a[high]
        var i = low

        for j in low..<high {
            if areInIncreasingOrder(a[j], pivot) {
                a.swapAt(i, j)
                i += 1
            }
        }

        a.swapAt(i, high)
        return i
    }
}

guard var numbers = parseIntegers(from: CommandLine.arguments) else {
    print(usage)
    exit(1)
}

numbers.quickSort(by: <)

print(numbers.map(String.init).joined(separator: ", "))

Quick Sort in Swift was written by:

• Ștefan-Iulian Alecu

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

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