使用python实现链表与反转

链表记录了头节点与尾节点，是为了方便末尾添加时，不在遍历链表而设置的。反转的思想是设置一个前驱节点为None，首节点指向None，下一个节点指向前一个节点即可。

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

    def __str__(self):
        return f'<Node:{self.data}>'


class LinkedList(object):
    def __init__(self):
        self.head = None
        self.last = None

    def is_empty(self):
        if not self.head:
            return True

    def append(self, data):
        if self.is_empty():
            self.head = Node(data)
            self.last = self.head
        else:
            self.last.next = Node(data)
            self.last = self.last.next
            # cur = self.head
            # while cur.next:
            #     cur = cur.next
            # cur.next = Node(data)

    def iter_node(self):
        cur = self.head
        while cur:
            print(cur)
            cur = cur.next

    def last_node(self):
        return self.last

    def reverse(self):
        # 前驱节点
        pre = None
        # 当前节点
        cur = self.head
        # 头尾节点交换
        self.head, self.last = self.last, self.head
        while cur:
            # 记录后驱节点
            tmp = cur.next
            # 后驱节点指向前驱节点
            cur.next = pre
            # 当前节点成为前驱节点
            pre = cur
            cur = tmp

测试结果：

# A -> B -> C -> D
l = LinkedList()
l.append('A')
l.append('B')
l.append('C')
l.append('D')
l.iter_node()
l.reverse()
l.iter_node()
# D -> C -> B -> A