单链表反转

class Node(object):
    def __init__(self, value=None, next=None):
        self.value = value
        self.next = next

def reverse(head):
    if head == None or head.next == None:
        return head
    pre = None
    next = None
    while head != None:
        next = head.next
        head.next = pre
        pre = head
        head = next
    return pre

if __name__ == '__main__':
    l1 = Node(1)
    l1.next = Node(2)
    l1.next.next = Node(3)
    l2 = reverse(l1)
    print(l2.value, l2.next.value, l2.next.next.value)