Python实现链表倒序（带头指针）

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

def reverseList(self, head):
    if head == None or head.next == None:
        return head
    p = head.next
    while p.next:
        p1 = p.next
        p.next = head
        head, p = p, p1
    p.next = head
    return p