Question

(Python) Define a function makeTwoWay that expects a singly linked structure as its argument. The function builds and returns a doubly linked structure that contains the items in the singly linked structure. (Note: The function should not alter the argument's structure.)

node.py source code:

"""
File: node.py

Node classes for one-way linked structures and two-way
linked structures.
"""

class Node(object):

    def __init__(self, data, next = None):
        """Instantiates a Node with default next of None"""
        self.data = data
        self.next = next

class TwoWayNode(Node):

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

# Just an empty link
node1 = None

# A node containing data and an empty link
node2 = Node("A", None)

# A node containing data and a link to node2
node3 = Node("B", node2)

Answer 1

#Phython code

class Node(object):

    def __init__(self, data, next = None):
        """Instantiates a Node with default next of None"""
        self.data = data
        self.next = next

class TwoWayNode(Node):

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

def makeTwoWay(sll):
    head = None
    prev = None
    while sll != None:
        if head == None:
            head = TwoWayNode(sll.data , prev)
            prev = head
        else:
            prev.next = TwoWayNode(sll.data , prev)
            prev = prev.next

        sll = sll.next

    return head
      
      

# Just an empty link
node1 = None

# A node containing data and an empty link
node2 = Node("A", None)

# A node containing data and a link to node2
node3 = Node("B", node2)

head = makeTwoWay(node3)

#Screeshot