leetcode解题-reverse linked list

class (object):
    def __init__(self, x):
        self.val = x
        self.next = None


class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        last = None
        while head:
            next = head.next
            head.next = last
            last = head
            head = next
        return last