实现单链表的倒置（两种方法）

# conding:utf8
class Node():
    def __init__(self, _item):
        self.item = _item
        self.next = None


class Link():
    def __init__(self):
        self._head = None

    def append(self, _item):
        node = Node(_item)
        cur = self._head
        pre = None
        if cur == None:
            self._head = node
            return
        while cur:
            pre = cur
            cur = cur.next
        pre.next = node

    def travel(self):
        cur = self._head
        while cur:
            print(cur.item)
            cur = cur.next

    # 方式一：三个变量实现单链表倒置
    def reverse1(self):
        pre = None
        cur = self._head
        next_node = cur.next
        while cur:
            cur.next = pre
            pre = cur
            cur = next_node
            if next_node:
                next_node = next_node.next
        self._head = pre

    # 方式二：两个变量实现单链表的倒置
    def reverse2(self):
        pre = None
        cur = self._head
        while cur:
            temp = cur.next
            cur.next = pre
            pre = cur
            cur = temp
        self._head = pre


if __name__ == "__main__":
    link = Link()
    link.append(1)
    link.append(2)
    link.append(3)
    link.travel()
    print("---------------------------")
    link.reverse1()
    link.travel()

1
2
3
---------------------------
3
2
1