testingMinimumMaximum.swift

import Foundation

private let measurements = 1_000
private func measureExecutionTime(_ title: String, f: (() -> Any) ) {
    let start = Date()
    var result: Any?
    for _ in 0..<measurements {
        result = f()
    }
    let end = Date()
    let duration = end.timeIntervalSince(start)
    print("\(title.padding(toLength: 10, withPad: " ", startingAt: 0)) | \("\(duration)".padding(toLength: 21, withPad: " ", startingAt: 0)) | \(result ?? "OHNO")")
}

/********************* start setup *********************/
private extension MutableCollection where Index == Int, IndexDistance == Int {
    mutating func shuffle() {
        guard count > 1 else { return }
        let random: (Int) -> Int = { Int(arc4random_uniform(UInt32($0))) }
        for i in 0..<count - 1 {
            let j = random(count - i) + i
            guard i != j else { continue }
            swap(&self[i], &self[j])
        }
    }
}

private let input = ["zero","one","two","three","four","five","six","seven","eight","nine","ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen","seventeen","eighteen","nineteen","twenty","twentyone","twentytwo","twentythree","twentyfour","twentyfive","twentysix","twentyseven","twentyeight","twentynine","thirty","thirtyone","thirtytwo","thirtythree","thirtyfour","thirtyfive","thirtysix","thirtyseven","thirtyeight","thirtynine","forty","fortyone","fortytwo","fortythree","fortyfour","fortyfive","fortysix"]
private let rand = { input[Int(arc4random_uniform(UInt32(input.count)))] }
private var arr: [String] = []
for i in 0..<1000 {
    arr.append(rand())
}
arr.shuffle()

/********************* start measuring *********************/
measureExecutionTime("orig") {
    func minimumMaximum<T: Comparable>(_ array: [T]) -> (minimum: T, maximum: T)? {
        var array = array
        guard !array.isEmpty else {
            return nil
        }

        var minimum = array.first!
        var maximum = array.first!

        let hasOddNumberOfItems = array.count % 2 != 0
        if hasOddNumberOfItems {
            array.removeFirst()
        }

        while !array.isEmpty {
            let pair = (array.removeFirst(), array.removeFirst())

            if pair.0 > pair.1 {
                if pair.0 > maximum {
                    maximum = pair.0
                }
                if pair.1 < minimum {
                    minimum = pair.1
                }
            } else {
                if pair.1 > maximum {
                    maximum = pair.1
                }
                if pair.0 < minimum {
                    minimum = pair.0
                }
            }
        }

        return (minimum, maximum)
    }
    return minimumMaximum(arr)!
}

measureExecutionTime("stride") {
    func minimumMaximum<T: Comparable>(_ array: [T]) -> (minimum: T, maximum: T)? {
        guard !array.isEmpty else {
            return nil
        }

        var minimum = array.first!
        var maximum = array.first!

        // if 'array' has an odd number of items, let 'minimum' or 'maximum' deal with the leftover
        let hasOddNumberOfItems = array.count % 2 != 0
        let start = hasOddNumberOfItems ? 1 : 0
        for i in stride(from: start, to: array.count, by: 2) {
            let pair = (array[i], array[i+1])

            if pair.0 > pair.1 {
                if pair.0 > maximum {
                    maximum = pair.0
                }
                if pair.1 < minimum {
                    minimum = pair.1
                }
            } else {
                if pair.1 > maximum {
                    maximum = pair.1
                }
                if pair.0 < minimum {
                    minimum = pair.0
                }
            }
        }

        return (minimum, maximum)
    }
    return minimumMaximum(arr)!
}

example output:

orig       | 0.503057956695557     | (minimum: "eight", maximum: "zero")
stride     | 0.0287469625473022    | (minimum: "eight", maximum: "zero")