MonatomicSequence.swift

enum Trend {
    case ascending
    case decending
}


func trend(for sequence: [Int]) -> Trend? {
    var trend: Trend?

    for (index, item) in sequence.enumerated() {
        guard index != 0 else {
            continue
        }

        if item > sequence[index - 1] && (trend == .ascending || trend == nil) {
            print("ascending")
            trend = .ascending
        } else if item < sequence[index - 1] && (trend == .decending || trend == nil) {
            print(index - 1)
            print(sequence[index - 1])
            print(item, "\n")
            trend = .decending
        } else {
            return nil
        }
    }

    return trend
}

trend(for: [4, 6, 8])

trend(for: [3, 2, 1])

trend(for: [1, 2, 1])