"""
File: abstractcollection.py
Copyright 2015 by 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
        self._modCount = 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, using []
        as delimiters."""
        return "[" + ", ".join(map(str, self)) + "]"

    def __eq__(self, other):
        """Returns True if self equals other,
        or False otherwise.
        Compares pairs of items in the two sequences
        generated by the iterators on self and other."""
        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 __add__(self, other):
        """Returns a new collection containing the contents
        of self and other."""
        result = type(self)(self)
        for item in other:
            result.add(item)
        return result

    def count(self, item):
        """Returns the number of instance of item in self."""
        counter = 0
        for nextItem in self:
            if item == nextItem: counter += 1
        return counter

    # These methods track and update the modCount, which is used to
    # prevent mutations within the context of an iterator (for loop)

    def getModCount(self):
        """Returns the number of modifications to the collection."""
        return self._modCount

    def incModCount(self):
        """Increments the number of modifications to the collection."""
        self._modCount += 1



 

# This program exercises graphs.

 

# Replace any "<your code>" comments with your own code statement(s)

# to accomplish the specified task.

# Do not change any other code.

 

# The following files must be in the same folder:

#  abstractcollection.py

#  graph.py

 

from graph import LinkedDirectedGraph

 

# Part 1:

# Complete the following function:

def topologicalSort(graph): 

    # <your code>

 

graph = LinkedDirectedGraph()

 

# The graph represents the following course prerequisites:

# A requires nothing

# B requires nothing

# C requires A

# D requires A, B, and C

# E requires C

# F requires B and D

# G requires E and F

# H requires C, F, and G

 

# Part 2:

# Add the vertices:

# <your code>

 

# Part 3:

# Add the edges:

# <your code>

 

print("Graph:")

print(graph)

print()

 

print("Courses:")

# Part 4:

# Display each vertex on a separate line:

# <your code>

print()

 

print("Prerequisites:")

# Part 5:

# Display each edge on a separate line:

# <your code>

print()

 

print("One possible order to take the courses:")

# Part 6:

# Display the courses in prerequisite (topological) order:

# <your code>

print()