python 双链表

双链表是一种链式数据结构，每个节点有两个指针，一个指向前一个节点，一个指向后一个节点。相比于单链表，双链表可以双向遍历，查找效率更高。以下是Python实现双链表的代码：

class Node(object):
    def __init__(self, val, p=0):
        self.data = val
        self.next = p
        self.prev = p

class DoubleLinkList(object):
    def __init__(self):
        self.head = 0

    def isEmpty(self):
        return self.head == 0

    def length(self):
        p = self.head
        length = 0
        while p != 0:
            length += 1
            p = p.next
        return length

    def travel(self):
        p = self.head
        while p != 0:
            print(p.data)
            p = p.next

    def add(self, val):
        node = Node(val)
        if self.isEmpty():
            self.head = node
        else:
            node.next = self.head
            self.head.prev = node
            self.head = node

    def append(self, val):
        node = Node(val)
        if self.isEmpty():
            self.head = node
        else:
            p = self.head
            while p.next != 0:
                p = p.next
            p.next = node
            node.prev = p

    def insert(self, pos, val):
        if pos <= 0:
            self.add(val)
        elif pos > self.length() - 1:
            self.append(val)
        else:
            node = Node(val)
            p = self.head
            count = 0
            while count < pos - 1:
                count += 1
                p = p.next
            node.prev = p
            node.next = p.next
            p.next.prev = node
            p.next = node

    def remove(self, val):
        if self.isEmpty():
            return
        p = self.head
        if p.data == val:
            if p.next == 0:
                self.head = 0
            else:
                p.next.prev = 0
                self.head = p.next
            return
        while p.next != 0:
            if p.next.data == val:
                p.next = p.next.next
                if p.next != 0:
                    p.next.prev = p
                return
            p = p.next