LeetCode 206 反转链表

# 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 not head or not head.next:
            return head
        l = head
        r = head.next
        head.next = None
        while(r):
            t = r.next
            r.next = l
            l = r
            r = t
        return l