leetcode206. Reverse Linked List

Reverse a singly linked list.

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def reverseList(self, head):        """        :type head: ListNode        :rtype: ListNode        """        if head==None:            return None        p1=None        p2=head        while(p2):            tmp=p2.next            p2.next=p1            p1=p2            p2=tmp        return p1