LeetCode - 206. Reverse Linked List

Q：

Reverse a singly linked list.

Hint:

A linked list can be reversed either iteratively or recursively. Could you implement both?

A：

# 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
"""
pre = None
while head:
current = head
head = head.next
current.next = pre
pre = current
return pre