ReverseLL.py

# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = None

class Solution(object):
 def reverseList(self, head):
 """
 :type head: ListNode
 :rtype: ListNode
 """
 reversed = self.reverseNodes(head, None)
 return reversed
 
 def reverseNodes(self, forward_head, backward_head):
 if not forward_head:
 return backward_head
 forward_head_next = forward_head.next
 backward_head_next = forward_head
 backward_head_next.next = backward_head
 return self.reverseNodes(forward_head_next, backward_head_next)