python---双链表的常用操作

class Node(object):
    """结点"""

    def __init__(self, data):
        self.data = data
        self.pre = None
        self.next = None

class DoubleLinkList(object):
    """双链表"""

    def __init__(self, node=None):
        self.__head = node

    def is_empty(self):
        """判断链表是否为空"""
        return self.__head is None

    def length(self):
        """链表的长度"""
        count = 0
        cur = self.__head
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur is not None:
            print(cur.data, end="")
            cur = cur.next
        print()

    def add(self, item):
        """头插"""
        node = Node(item)
        # 空链表头插
        if self.is_empty():
            self.__head = node
        # 非空链表头插
        else:
            node.next = self.__head
            self.__head.pre = node
            self.__head = node

    def append(self, item):
        """尾插"""
        node = Node(item)
        # 空链表尾插
        if self.is_empty():
            self.__head = node
        # 非空链表尾插
        else:
            cur = self.__head
            # 找到最后一个结点
            while cur.next is not None:
                cur = cur.next
            cur.next = node
            node.pre = cur

    def insert(self, pos, item):
        """指定位置插入"""
        if pos <= 0:
            self.add(item)
        elif pos > self.length() - 1:
            self.append(item)
        else:
            node = Node(item)
            cur = self.__head
            count = 0
            # 找到指定位置的前一个结点
            while count < pos - 1:
                cur = cur.next
                count += 1
            node.next = cur.next
            node.pre = cur
            cur.next = node
            node.next.pre = node

    def remove(self, item):
        """删除指定结点"""
        cur = self.__head
        while cur is not None:
            # 找到要删除的结点
            if cur.data == item:
                # 如果要删除的结点是头结点
                if cur == self.__head:
                    self.__head = cur.next
                    # 判断链表是否只有一个结点
                    if cur.next:
                        cur.next.pre = None
                # 要删除的结点不是头结点
                else:
                    cur.pre.next = cur.next
                    # 判断要删除的结点是否是尾结点
                    if cur.next:
                        cur.next.pre = cur.pre
                return
            else:
                cur = cur.next

    def search(self, item):
        """查找结点是否存在"""
        cur = self.__head
        while cur is not None:
            if cur.data == item:
                return True
            else:
                cur = cur.next
        return False

if __name__ == '__main__':
    sll = DoubleLinkList()
    print(sll.is_empty())
    print(sll.length())
    sll.add(1)
    sll.remove(1)
    print(sll.is_empty())
    print(sll.length())
    sll.append(2)
    sll.append(3)
    sll.append(4)
    sll.append(5)
    sll.travel()  # 2345
    print(sll.length())  # 4
    sll.add(99)  # 99 2345
    sll.travel()
    print(sll.length())  # 5
    print(sll.search(6))  # False
    print(sll.search(4))  # True
    sll.remove(5)
    sll.travel()  # 99 234