'''
CSCI 204.01 Exam 1 review exercise
Divide the students into groups and each group solves one proble, then exchange their ideas
or solution.
1. Write a Python function that can remove all nodes with specific data value in a doubly linked list.
2. Write a Python function that can count the number of nodes in a circular linked list with a specific data value.
3. Write an operator overloading function __sub__ that removes a node with specified value in a singly linked list.
4. Write a recursive function to compute the length of a singly linked list.
5. Write a child class with a constructor, string function, length function that inherits information from a parent class.
'''

'''
This is the start file for P4 (doubly linked list removal)
'''
class DLinkedList:
    """ A user defined doubly linked list"""
    def __init__(self):
        self.head = None
        self.tail = None

    def __str__(self):
        """ String function """
        s = '['
        h = self.head
        while h != None:
            s += str(h.data)
            h = h.next
            if h != None:
                s += ', '
        s += ']'
        return s

    def __len__(self)
        """count length (the len() function recursively"""
        pass
        
    def insert(self, node):
        """ Insert a value 'data'"""

        if self.head == None:       # empty list
            self.head = node
            self.tail = node
        else:                       # insert after tail
            self.tail.next = node
            node.prev = self.tail
            self.tail = node


class DListNode:
    """ The node class for list notes"""
    def __init__(self, data):
        self.data = data
        self.next = None
        self.prev = None