Reverse a singly linked list.
# 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 """ if head is None or head.next is None: return head elif head.next.next is None: t = head.next head.next.next = head head.next = None return t else: t = self.reverseList(head.next) head.next.next = head head.next = None return t