1. Node Applications in Abstract Data Types
Jack Tompkins
CSC Introduction to Data Structures

2. Queue Fields head, tail, size
We need to decide which end of ADT to use as the rear and which to use as the front implementing First In First Out (FIFO) behavior
We enter the queue at the rear – enqueue will add a node making it the tail
and exit from the head –dequeue will remove and return the head for our lab, raises an IndexError if dequeue is attempted on an empty queue

3. Doubly-Linked Node A node keeps track of What is next AND
What is previous

4. 1
class Queue: # implemented using a Node in Lab 5 2
    def __init__(self): 3
       pass 4 5
    def is_empty(self): 6
        pass 7 8
    def enqueue(self, item): 9 10 11
    def dequeue(self): # raises IndexError if queue is initially empty 12 13 14
    def size(self): 15 16 17
   def peek(self): 18
pass 19

5. 1
class Queue: # implemented using a DLL based on DLNode in Lab 3 2
    def __init__(self): 3
       pass 4 5
    def isEmpty(self): 6
        pass 7 8
    def enqueue(self, item): 9 10 11
    def dequeue(self): 12 13 14
    def size(self): 15

6. 1
class Node: 2
    def __init__(self, value): 3
""“ Initializes a node by setting its data to value and 4
prev and next to None 5
:return: The reference for self 6
        """ 7
        self.data = value 8
self.prev = None 9
   self.next = None 10
# setters and getters written but not used for this application

7. 1
class DoublyLinkedNode: 2
    def __init__(self, value): 3
""“ Initializes a node by setting its data to value and 4
prev and next to None 5
:return: The reference for self 6
        """ 7
        self.data = value 8
self.prev = None 9
   self.next = None

8. 1
class Deque(Queue): # implemented by extending the Queue class in Lab 5 2
    def __init__(self): 3
       super().__init__() 4 5
    def peek_back(self): 6
        if self.tail: 7
return self.tail.data 8
    def enqueue_front(self, item): 9
       new_head = Node(item) 10
if self.is_empty(): 11
     self.head = new_head 12
       self.tail = new_head 13
else: 14
self.head.prev= new_head 15
new_head.next = self.head 16
self.head = new_head 17
self.size += 1

9. 1
class Deque(Queue): # implemented by extending the Queue class in Lab 5 18 19
def dequeue_back(self): 20
       if self.is_empty(): 21
raise IndexError(‘attempted dequeue_back on an empty deque’) 22 23
    data = self.tail.data 24
       if self.tail.prev: 25
     self.tail = self.tail.prev 26
self.tail.next = None 27
self.size -= 1 28
return data

10. Testing the Node based Queue & Deque
Place this in a PyCharm Project folder with node.py, queue.py, and deque.py

11. Using a Singly-Linked List Using a Doubly-Linked Node
Summary
Using a Python List
Using a Singly-Linked List
Using a Doubly-Linked Node
Stack
Push
O(1)
Pop
Queue
Enqueue
O(n)
O(1)*
Dequeue
Deque
AddFront
AddRear
RemoveFront
RemoveRear
List
Add/Remove End
O(1)/O(n)
Add/Remove Front
Add/Remove index k
Get at index k