双向链表的Python代码

双向链表（Doubly Linked List）是一种数据结构，其中每个节点都有两个指针，分别指向前一个节点和后一个节点。在Python中，我们可以这样实现一个简单的双向链表：

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

class DoublyLinkedList:
    def __init__(self):
        self.head = None

    # 插入节点到链表头部
    def insert_at_start(self, data):
        new_node = Node(data)
        if self.head is not None:
            new_node.next = self.head
            self.head.prev = new_node
        self.head = new_node

    # 在链表尾部插入节点
    def append(self, data):
        new_node = Node(data)
        if self.head is None:
            self.head = new_node
            return
        last_node = self.head
        while last_node.next:
            last_node = last_node.next
        last_node.next = new_node
        new_node.prev = last_node

    # 删除指定节点
    def delete(self, key):
        current = self.head
        if current and current.data == key:
            self.head = current.next
            if self.head:
                self.head.prev = None
            return
        prev = None
        while current and current.data != key:
            prev = current
            current = current.next
        if current is None:
            return
        prev.next = current.next
        if current.next:
            current.next.prev = prev

    # 遍历链表并打印节点值
    def print_list(self):
        current = self.head
        while current:
            print(current.data, end=" <-> ")
            current = current.next
        print("None")

# 示例用法
dll = DoublyLinkedList()
dll.insert_at_start(1)
dll.insert_at_start(2)
dll.append(3)
dll.print_list()  # 输出: 2 <-> 1 <-> 3 <-> None