A simple swift sequence/iterator for the 3n+1 problem

threeNPlusOne.swift

class threeNPlusOne: Sequence, IteratorProtocol {
    var n: UInt
    
    init(withStartNumber startN: UInt) {
        n = startN * 2 // multiply by 2 so that n is a even number and will be devided by two in the first next() call
    }
    
    func next() -> UInt? {
        if n % 2 == 0 {       // even
            n /= 2
        } else {
            n = (3 * n) + 1   // odd
        }
        return n
    }
    
    func contains(_ element: UInt) -> Bool {
        var oneCount = 0 // the only known endless loop is 4 - 2 - 1
        
        while oneCount < 2 {
            let currentNumber = self.next()
            
            if currentNumber == element {
                return true
            } else if currentNumber == 1 {
                oneCount += 1
            }
        }
        return false
    }
    
    func enteredKnownEndlessLoop() -> Bool {
        return n == 1 || n == 2 || n == 4
    }
}

var iterator = threeNPlusOne(withStartNumber: 18);

while (true) {
    let currentNumber = iterator.next()!
    print(currentNumber)
    if iterator.enteredKnownEndlessLoop() { break }
}

print(threeNPlusOne(withStartNumber: 18).contains(17))