Question

python

Programming assignment: Let's think about doubly-linked lists. Define a class ListNode2, with three attributes: item, left, and rightL. Left link points to the previous node in the list, right link points to the next node in the list. You can also add the display method to this class (like we did it in class for the ListNode class). Then test your class. For example, create a linked list of 5 values: 34,1, 23, 7, and 10. Display it. Then insert new value, say 8 between 34 and 1 (this time you will have to take care of links pointing to the previous and next node), display the resulting list. Then delete an element, say 7, update the links and display the new list. Use this draft: ListNode2_forStudents.py

Answer 1

Code:

class ListNode2():

    def __init__(self, item=None, leftL=None, rightL=None):

        self.item = item

        self.leftL = leftL

        self.rightL = rightL

        if leftL != None:

            leftL.rightL = self

        if rightL != None:

            rightL.leftL = self

    def __str__(self):

        return str(self.item)

def printLR(headNode):

    node = headNode

    while node is not None:

        print(node.item)

        node = node.rightL

    print("end of linked list")

def printRL(tailNode):

    node = tailNode

    listV = []

    while node is not None:

        listV.append(node.item)

        node = node.leftL

    listV = listV[::-1]

    print("here is list of elements, following left links:", listV)

    return listV

# Testing

n5 = ListNode2(10)

n4 = ListNode2(7, None, n5)

n3 = ListNode2(23, None, n4)

n2 = ListNode2(1, None, n3)

n1 = ListNode2(34, None, n2)

# printing

printLR(n1)

printRL(n5)

# Inserting 8 btw 34 and 1

print("\nInserting 8...")

n6 = ListNode2(8, n1, n2)

# printing

printLR(n1)

printRL(n5)

# Deleting 7

print("\nDeleting 7....")

n3.rightL = n5

n5.leftL = n3

del n4

# printing

printLR(n1)

printRL(n5)

Output:

34
1
23
7
10
end of linked list
here is list of elements, following left links: [34, 1, 23, 7, 10]

Inserting 8...
34
8
1
23
7
10
end of linked list
here is list of elements, following left links: [34, 8, 1, 23, 7, 10]

Deleting 7....
34
8
1
23
10
end of linked list
here is list of elements, following left links: [34, 8, 1, 23, 10]