func absolutePermutation(n: Int, k: Int) -> [Int] {
    var results: [Int] = [Int]()
    var isUpper: Bool = false
    
    if k == 0 { return Array(1 ... n) }
    
    for number in 0 ... n - 1 {        
        if number % k == 0 { isUpper = !isUpper }
        
        if isUpper { results.append((number + 1) + k) }
        else { results.append((number + 1) - k) }
    
        if results.last! > n { return [-1] }
    }
    return results
}