# Libraries Included:
# Numpy, Scipy, Scikit, Pandas

print "Hello, world!"

class Node(object):
    def __init__(self, val=None, next=None):
        self.val = val
        self.next = next

    def append(self, next):
        if not isinstance(next, Node):
            raise RuntimeError("Not node!")
        self.next = next
        return next


def print_linked_list(node):
    print node.val
    if node.next:
        print_linked_list(node.next)


def reverse(node):
    if not node:
        return node
    previous = None
    current = node
    while current:
        next = current.next
        current.next = previous
        previous = current
        current = next
    return previous


def reverse_k_only(node, k):
    if not node:
        return node
    previous = None
    current = node
    end_of_k = current
    while current and k > 0:
        next = current.next
        current.next = previous
        previous = current
        current = next
        k -= 1
    end_of_k.next = current
    return previous, end_of_k


def reverse_in_k_group(node, k):
    if k == 0:
        return node
    start, end_of_k = reverse_k_only(node, k)

    while end_of_k.next:
        old_end_of_k = end_of_k
        new_start, end_of_k = reverse_k_only(end_of_k.next, k)
        old_end_of_k.next = new_start
    return start


def reverse_in_variable_k_group(node, k):
    start, end_of_k = reverse_k_only(node, k)
    k -= 1

    while end_of_k.next and k > 0:
        old_end_of_k = end_of_k
        new_start, end_of_k = reverse_k_only(end_of_k.next, k)
        old_end_of_k.next = new_start
        k -= 1
    if k == 0:
        end_of_k.next = None
    return start


head = Node(1)
next = head
for i in range(2,10):
    next = next.append(Node(i))


print_linked_list(head)

reversed = reverse_in_variable_k_group(head, 7)

print_linked_list(reversed)