func shuffle(arr) {
    if arr.Length() % 2 != 0 {
        throw @InvalidValue(arr.Length())
    }
    var half = arr.Length() / 2
    var result = Array.Empty(arr.Length())
    var (t, l, r) = (0, 0, half)

    while l < half {
        result[t] = arr[l]
        result[t+1] = arr[r]
        l += 1
        r += 1
        t += 2
    }
    result
}

func arrayEqual(xs, ys) {
    if xs.Length() != ys.Length() {
        return false
    }
    for i in xs.Indices() {
        if xs[i] != ys[i] {
            return false
        }
    }
    return true
}

func shuffleThrough(original) {
    var copy = original.Clone()

    while true {
        copy = shuffle(copy)
        yield copy
        if arrayEqual(original, copy) {
            break
        }
    }
}

for input in yields { 8, 24, 52, 100, 1020, 1024, 10000} {
    var numbers = [1..input]
    print("\(input) cards: \(shuffleThrough(numbers).Length())")
}