(e) (6 marks)

Suppose we want to add functionality to the cinema priority queue implementation that allows the user to change the priority of an item in the queue. You may assume the items are unique.

Complete the problem definition below, stating any further assumptions you make. If you make no assumptions, say so.

Write your answer here

Operation: change_priority Inputs/Outputs: queue, a CinemaPriorityQueue Inputs: item, an object, new priority, an integer Preconditions: Postconditions: Assumptions:

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QUESTIOIN BEFORE

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(c) (10 marks)

Edit the insert function in the code below to convert your algorithm into Python code. You must observe the coding style guidance in Chapter 5.3 and Chapter 10.3.

In [ ]:

class CinemaPriorityQueue:

 """A linked list implementation of an unbounded min-priority queue."""

 class Node:

 """A node in a linked list."""

 def __init__(self, item: object, priority_value: int) -> None:

 """Initialise the node with the given item and priority value."""

 self.item = item

 self.priority = priority_value

 self.next = None

 def __init__(self) -> None:

 """Initialise the queue to be empty."""

 self.head = None

 def is_empty(self) -> bool:

 """

 Preconditions: true

 Postconditions: the output is true if the queue is empty, false otherwise

 """

 return self.head == None

 def print(self) -> None:

 """Print out the queue"""

 if self.head == None:

 print('The queue is empty')

 else:

 current = self.head

 while current != None:

 print(current.item, current.priority)

 current = current.next

 def insert(self, item: object, priority_value: int) -> None:

 """Insert item according to priority.

 Preconditions: true

 Postconditions: post-self is the sequence

 pre-self with item inserted after

 the last item in self with the same priority

 """

 pass

 #*Write your code solution here*

(d) (12 marks)

We have provided a print operation print() that you can use to print out the queue. Test your code. You may use additional print statements to explain what you are testing with each test. Make sure you test for each of the three cases:

• insert into an empty queue
• insert at the front of the queue
• insert after some existing node.