e_it_opposite.py

# Comment it before submitting
class DoubleConnectedNode:
    def __init__(self, value, next=None, prev=None):
        self.value = value
        self.next = next
        self.prev = prev


def solution(node):
    previuos_node = node
    next_node = node.next
    previuos_node.next = None
    previuos_node.prev = next_node
    while next_node is not None:
        next_node.prev = next_node.next
        next_node.next = previuos_node
        previuos_node = next_node
        next_node = next_node.prev
    return previuos_node


def test():
    node3 = DoubleConnectedNode("node3")
    node2 = DoubleConnectedNode("node2")
    node1 = DoubleConnectedNode("node1")
    node0 = DoubleConnectedNode("node0")

    node0.next = node1

    node1.prev = node0
    node1.next = node2

    node2.prev = node1
    node2.next = node3

    node3.prev = node2
    new_head = solution(node0)
    # result is new_head == node3
    # node3.next == node2
    # node2.next == node1 node2.prev == node3
    # node1.next == node0 node1.prev == node2
    # node0.prev == node1


if __name__ == '__main__':
    test()