Question

In python -

Implement a doubly linked circular linked list of Node objects called CircularDoublyLinkedList. The data of each Node in the list is an integer. You will collect measurements for:

1. An already sorted linked list
2. An already sorted linked list in descending order
3. A linked list containing random data

Answer 1

# A complete working Python program to demonstrate all
# insertion methods
  
# A linked list node
class Node:

    # Constructor to create a new node
    def __init__(self, data):
        self.data = data
        self.next = None
        self.prev = None
  
# Class to create a Doubly Linked List
class DoublyLinkedList:
  
    # Constructor for empty Doubly Linked List
    def __init__(self):
        self.head = None
  
    # Given a reference to the head of a list and an
    # integer, inserts a new node on the front of list
    def push(self, new_data):
  
        # 1. Allocates node
        # 2. Put the data in it
        new_node = Node(new_data)
  
        # 3. Make next of new node as head and
        # previous as None (already None)
        new_node.next = self.head
  
        # 4. change prev of head node to new_node
        if self.head is not None:
            self.head.prev = new_node
  
        # 5. move the head to point to the new node
        self.head = new_node
  
    # Given a node as prev_node, insert a new node after
    # the given node
    def insertAfter(self, prev_node, new_data):
  
        # 1. Check if the given prev_node is None
        if prev_node is None:
            print "the given previous node cannot be NULL"
            return
  
        # 2. allocate new node
        # 3. put in the data
        new_node = Node(new_data)
  
        # 4. Make net of new node as next of prev node
        new_node.next = prev_node.next
  
        # 5. Make prev_node as previous of new_node
        prev_node.next = new_node
  
        # 6. Make prev_node ass previous of new_node
        new_node.prev = prev_node
  
        # 7. Change previous of new_nodes's next node
        if new_node.next is not None:
            new_node.next.prev = new_node
  
    # Given a reference to the head of DLL and integer,
    # appends a new node at the end
    def append(self, new_data):
  
        # 1. Allocates node
        # 2. Put in the data
        new_node = Node(new_data)
  
        # 3. This new node is going to be the last node,
        # so make next of it as None
        new_node.next = None
  
        # 4. If the Linked List is empty, then make the
        # new node as head
        if self.head is None:
            new_node.prev = None
            self.head = new_node
            return
  
        # 5. Else traverse till the last node
        last = self.head
        while(last.next is not None):
            last = last.next
  
        # 6. Change the next of last node
        last.next = new_node
  
        # 7. Make last node as previous of new node
        new_node.prev = last
  
        return
  
    # This function prints contents of linked list
    # starting from the given node
    def printList(self, node):
  
        print "\nTraversal in forward direction"
        while(node is not None):
            print " % d" %(node.data),
            last = node
            node = node.next
  
        print "\nTraversal in reverse direction"
        while(last is not None):
            print " % d" %(last.data),
            last = last.prev
  
# Driver program to test above functions
  
# Start with empty list
llist = DoublyLinkedList()
  
# Insert 6. So the list becomes 6->None
llist.append(6)
  
# Insert 7 at the beginning.
# So linked list becomes 7->6->None
llist.push(7)
  
# Insert 1 at the beginning.
# So linked list becomes 1->7->6->None
llist.push(1)
  
# Insert 4 at the end.
# So linked list becomes 1->7->6->4->None
llist.append(4)
  
# Insert 8, after 7.
# So linked list becomes 1->7->8->6->4->None
llist.insertAfter(llist.head.next, 8)
  
print "Created DLL is: ",
llist.printList(llist.head)