almata / combinatorics Goto Github PK

Hey there, this repository implements exactly what I've been looking for, but I didn't really like the fact that it's implemented with a struct and generic static functions.

I've swiftly (hehe) implemented a protocol-oriented version of the permutationsWithRepetition function as an extension of the Collection type. Here's the code for a small working example:

let set : Set = [true,false]
let array : Array = [true,false]

extension Collection {
    func permutationsWithRepetition(length n:UInt) -> [[Element]] {
        guard n > 0 else {
            return [[]]
        }
        
        return self.map{element in self.permutationsWithRepetition(length: n - 1).map{[element] + $0}}.reduce([],+)
    }
}

print(set.permutationsWithRepetition(length: 2))
print(array.permutationsWithRepetition(length: 2))

Is there a reason why you've chosen static functions? What do you think about using protocol extensions instead? If you're interested, I'll gladly help porting the existing code to extensions.

CV

Could you implement the generator pattern? Instead of returning all data at once, return the next one once the next() method is called.