Solution for day 5

import Foundation

let argument = "REPLACE WITH YOUR INPUT"

public extension Character {
    public func swappedcased() -> Character {
        let lower = String(self).lowercased().first!
        if lower == self {
            return String(self).uppercased().first!
        } else {
            return lower
        }
    }
}


func react(on string: String) -> String {
    return string.reduce("") { (result, character) -> String in
        if let lastInsertedCharacter = result.last, lastInsertedCharacter == character.swappedcased() {
            return String(result.dropLast())
        }

        return result + String(character)
    }
}

func product(from string: String) -> Int {
    return react(on: string).count
}

var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".map { $0 }
var products = [Int]()

for character in alphabet {
    let string = argument.replacingOccurrences(of: String(character), with: "")
        .replacingOccurrences(of: String(character).lowercased(), with: "")

    products.append(product(from: string))
}

print("Step 1: \(product(from: argument))")
if let step2 = products.min() {
    print("Step 2: \(step2)")
}

Remove dependencies