Answered: Test it by: Add numbers from 13 to 23…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

python help.

Write a LikedQueue (code at bottom)

Test it by:

Add numbers from 13 to 23 in the queue.
Print the length of the queue
Check if the queue is empty
Show the item at the front of the queue
Remove the first item in the queue
Add 100 to the queue
Remove all items in the queue
Check if the queue is empty

"""
File: linkedqueue.py
Author: Ken Lambert
"""
from node import Node
from abstractcollection import AbstractCollection
class LinkedQueue(AbstractCollection):
"""A link-based queue implementation."""
# Constructor
def __init__(self, sourceCollection = None):
"""Sets the initial state of self, which includes the
contents of sourceCollection, if it's present."""
self.front = self.rear = None
AbstractCollection.__init__(self, sourceCollection)
# Accessor methods
def __iter__(self):
"""Supports iteration over a view of self."""
pass
def peek(self):
"""
Returns the item at the front of the queue.
Precondition: the queue is not empty.
Raises: KeyError if the stack is empty."""
if self.isEmpty():
raise KeyError("The queue is empty.")
return self.front.data
# Mutator methods
def clear(self):
"""Makes self become empty."""
pass
def add(self, item):
"""Adds item to the rear of the queue."""
newNode = Node(item, None)
if self.isEmpty():
self.front = newNode
else:
self.rear.next = newNode
self.rear = newNode
self.size += 1
def pop(self):
"""
Removes and returns the item at the front of the queue.
Precondition: the queue is not empty.
Raises: KeyError if the queue is empty.
Postcondition: the front item is removed from the queue."""
if self.isEmpty():
raise KeyError("The queue is empty.")
oldItem = self.front.data
self.front = self.front.next
if self.front is None:
self.rear = None

self.size -= 1
return oldItem

"

"""
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)

"
"

"""
File: abstractcollection.py
Author: Ken Lambert
"""
class AbstractCollection(object):
"""An abstract collection implementation."""
# Constructor
def __init__(self, sourceCollection = None):
"""Sets the initial state of self, which includes the
contents of sourceCollection, if it's present."""
self.size = 0
if sourceCollection:
for item in sourceCollection:
self.add(item)
# Accessor methods
def isEmpty(self):
"""Returns True if len(self) == 0, or False otherwise."""
return len(self) == 0
def __len__(self):
"""Returns the number of items in self."""
return self.size
def __str__(self):
"""Returns the string representation of self."""
return "[" + ", ".join(map(str, self)) + "]"
def __add__(self, other):
"""Returns a new bag containing the contents
of self and other."""
result = type(self)(self)
for item in other:
result.add(item)
return result
def __eq__(self, other):
"""Returns True if self equals other,
or False otherwise."""
if self is other: return True
if type(self) != type(other) or \
len(self) != len(other):
return False
otherIter = iter(other)
for item in self:
if item != next(otherIter):
return False
return True
def count(self, item):
"""Returns the number of instances of item in self."""
total = 0
for nextItem in self:
if nextItem == item:
total += 1
return total

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