nekedome / project-euler

solutions/problem17.py

"""
Project Euler Problem 17: Number Letter Counts
==============================================

.. module:: solutions.problem17
   :synopsis: My solution to problem #17.

The source code for this problem can be
`found here <https://bitbucket.org/nekedome/project-euler/src/master/solutions/problem17.py>`_.

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

If the numbers :math:`1` to :math:`5` are written out in words: one, two, three, four, five, then there are

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:math:`3 + 3 + 5 + 4 + 4 = 19` letters used in total.

If all the numbers from :math:`1` to :math:`1000` (one thousand) inclusive were written out in words, how many letters

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would be used?

.. note:: do not count spaces or hyphens. For example, :math:`342` (three hundred and forty-two) contains :math:`23`

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          letters and :math:`115` (one hundred and fifteen) contains :math:`20` letters. The use of "and" when writing

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          out numbers is in compliance with British usage.

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

Use the rules of English to construct the string representing the numbers from :math:`1` to :math:`1000`, remove

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characters not to be counted, then calculate the total length of that string.

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

.. literalinclude:: ../../solutions/problem17.py
   :language: python
   :lines: 39-
"""


def number_to_english(n: int) -> str:

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

    """ Translate an integer into words form

    :param n: the integer to translate
    :return: the English phrasing of :math:`n`

    >>> number_to_english(127)
    'one hundred and twenty-seven'
    """

    ones = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve",

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            "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"]
    tens = [None, None, "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"]

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    if 0 <= n < 20:
        return ones[n]
    elif 20 <= n <= 90 and n % 10 == 0:
        return tens[n // 10]
    elif 20 < n < 100:
        return tens[n // 10] + "-" + ones[n % 10]
    elif 100 <= n <= 900 and n % 100 == 0:
        return ones[n // 100] + " hundred"
    elif 100 < n < 1000:
        return ones[n // 100] + " hundred and " + number_to_english(n % 100)
    elif 1000 < n < 10000:
        pass
    elif n == 1000:
        return "one thousand"
    else:
        raise ValueError("unexpected input")


def solve():
    """ Compute the answer to Project Euler's problem #17 """
    target = 1000
    answer = 0
    for i in range(target):
        words = number_to_english(i + 1).replace(" ", "").replace("-", "")
        answer += len(words)
    return answer


expected_answer = 21124

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