nekedome / project-euler

solutions/problem19.py

"""
Project Euler Problem 19: Counting Sundays
==========================================

.. module:: solutions.problem19
   :synopsis: My solution to problem #19.

The source code for this problem can be
`found here <https://bitbucket.org/nekedome/project-euler/src/master/solutions/problem19.py>`_.

Problem Statement
#################

You are given the following information, but you may prefer to do some research for yourself.

* 1 Jan 1900 was a Monday.
*
  | Thirty days has September,
  | April, June and November.
  | All the rest have thirty-one,
  | Saving February alone,
  | Which has twenty-eight, rain or shine.
  | And on leap years, twenty-nine.
* A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.

This line is too long as per the coding-style (107/100).

How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

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Solution Discussion
###################

We could use Python's datetime module, but that feels too much like cheating :raw-html:`☺`

Instead, the above information will be used to count the number of Sundays falling on the first of the month.

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Solution Implementation
#######################

.. literalinclude:: ../../solutions/problem19.py
   :language: python
   :lines: 44-
"""


class Date(object):

The variable __class__ seems to be unused.

    """ A simple date abstraction representing a dd/mm/yyyy

    .. note:: the parameters are numbered in the natural way; i.e. ``day`` takes the range :math:`[1,31]`, ``month``

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              takes the range :math:`[1,12]` and ``year`` takes the range :math:`[0, 9999]`.

    :param day: the initial date value (day, or dd)
    :param month: the initial date value (month, or mm)
    :param year: the initial date value (year, or yyyy)
    """

    def __init__(self, day: int, month: int, year: int):
        # Basic parameter validation
        assert isinstance(day, int), "day must be an integer"
        assert isinstance(month, int), "month must be an integer"
        assert isinstance(year, int), "year must be an integer"
        assert 1 <= day <= 31, "day must be in [1, 31]"
        assert 1 <= month <= 12, "month must be in [1, 12]"
        assert 0 <= year <= 9999, "year must be in [0, 9999]"

        # Store the initial date provided
        self.day = day
        self.month = month
        self.year = year

    def __str__(self):
        """ String representation of a Date object """
        return "{}/{}/{}".format(self.day, self.month, self.year)

    def __le__(self, other: 'Date') -> bool:
        """ Test whether this ``Date`` instance is less than or equal to the `other` ``Date`` instance

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        :param other: the ``Date`` instance to compare against
        :return: ``True`` if the current ``Date`` is equal to or before the `other` ``Date`` instance

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        :return: ``False`` otherwise
        """

        if isinstance(other, Date):
            if self.year < other.year:
                return True  # earlier year
            elif self.year == other.year and self.month < other.month:
                return True  # same year, earlier month
            elif self.month == other.month and self.day < other.day:
                return True  # same year, same month, earlier day
        return False  # any other case

    def __add__(self, other: int) -> 'Date':
        """ Addition operator

        This class allows for integer values to be added to it. Semantically, this represents adding that integer number

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        of days to the current date value stored. The new date value will be returned by this operator.

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        :param other: the number of days to add to this ``Date`` instance
        :return: a new ``Date`` instance with `other` days added to the current value
        """

        if not isinstance(other, int):
            raise TypeError("unsupported operand type(s) for +")

        rv = Date(self.day, self.month, self.year)  # build new Date instance with the same value

The name rv does not conform to the variable naming conventions ((([a-z][a-z0-9_]{2,30})|(_[a-z0-9_]*))$).

        if rv.day + other > Date.days_to_a_month(rv.month, rv.year):
            other -= Date.days_to_a_month(rv.month, rv.year) - rv.day
            rv.day = 0
            rv.month += 1
        if rv.month > 12:
            rv.month = 1
            rv.year += 1
        rv.day += other
        return rv

    @staticmethod
    def leap_year(year: int) -> bool:
        """ Test whether the given `year` is a leap-year

        :param year: the year to test
        :return: ``True`` if `year` is a leap-year, ``False`` otherwise
        """

        return ((year % 4) == 0) and (((year % 100) != 0) or ((year % 400) == 0))

    @staticmethod
    def days_to_a_month(month, year):
        """ Compute the number of days in the month and year provided

        :param month: the given month
        :param year: the given year
        :return: the number of days in the given month and year
        """

        standard_days = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

        if month == 2 and Date.leap_year(year):

Unnecessary "else" after "return"

            return 29  # February has 29 days in a leap-year
        else:
            return standard_days[month - 1]


def solve():
    """ Compute the answer to Project Euler's problem #19 """

    lower_bound = Date(1, 1, 1901)
    upper_bound = Date(31, 12, 2000)
    current_date = Date(1, 1, 1900)
    answer = 0

    current_date += 6  # first Sunday after 1/1/1900

    # Skip over Sundays, one week at a time, until 1/1/1901
    while current_date <= lower_bound:
        current_date += 7  # next Sunday

    # Skip over Sundays, one week at a time, until 31/12/2000
    while current_date <= upper_bound:
        if current_date.day == 1:
            answer += 1  # this is a Sunday and the first of a month
        current_date += 7

    return answer


expected_answer = 171

The name expected_answer does not conform to the constant naming conventions ((([A-Z_][A-Z0-9_]*)|(__.*__))$).