Josephus Problem in Swift

Josephus Problem

in Swift

Welcome to the Josephus Problem 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 input the total number of people and number of people to skip."

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

extension Array {
    func argument(at index: Int) -> Element? {
        indices.contains(index) ? self[index] : nil
    }
}

func solveJosephus(_ n: Int, _ k: Int) -> Int {
    guard n > 0 else { return 0 }

    if k == 2 {
        let mostSignificantBit = 1 << (Int.bitWidth - 1 - n.leadingZeroBitCount)
        return 2 * (n - mostSignificantBit) + 1
    }

    return (2...n).reduce(0) { (survivor, i) in
        (survivor + k) % i
    } + 1
}

func parseInput(from args: [String]) -> (n: Int, k: Int)? {
    guard let rawN = args.argument(at: 1),
        let rawK = args.argument(at: 2),
        let n = Int(rawN.trimmed),
        let k = Int(rawK.trimmed),
        n > 0, k > 0
    else { return nil }

    return (n, k)
}

guard let (n, k) = parseInput(from: CommandLine.arguments) else {
    print(usage)
    exit(1)
}

print(solveJosephus(n, k))

Josephus Problem 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

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