"""

Definition of ListNode

class ListNode(object):

    def __init__(self, val, next=None):

        self.val = val

        self.next = next

"""

class Solution:

    """

    @param head: The first node of the linked list.

    @return: You should return the head of the reversed linked list.

                  Reverse it in-place.

    """

    def reverse(self, head):

        # write your code here

        if head is None: return None

        p = head

        cur = None

        pre = None

        while p is not None:

            cur = p.next

            p.next = pre

            pre = p

            p = cur

        return pre