Reverse a singly linked list.
Example:
Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL
思路:倒置链表,用前插法原地倒置.每次把头结点摘出来.
class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
pre = None
while head:
cur = head
head = head.next
cur.next = pre
pre = cur
return pre