Exercism v3 launches on Sept 1st 2021. Learn more! 🚀🚀🚀
Sign up Log in
Avatar of nicolemon

nicolemon's solution

to Sum Of Multiples in the Python Track

Published at Jul 21 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Given a number, find the sum of all the unique multiples of particular numbers up to but not including that number.

If we list all the natural numbers below 20 that are multiples of 3 or 5, we get 3, 5, 6, 9, 10, 12, 15, and 18.

The sum of these multiples is 78.

Exception messages

Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.

To raise a message with an exception, just write it as an argument to the exception type. For example, instead of raise Exception, you should write:

raise Exception("Meaningful message indicating the source of the error")

Running the tests

To run the tests, run the appropriate command below (why they are different):

  • Python 2.7: py.test sum_of_multiples_test.py
  • Python 3.4+: pytest sum_of_multiples_test.py

Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version): python -m pytest sum_of_multiples_test.py

Common pytest options

  • -v : enable verbose output
  • -x : stop running tests on first failure
  • --ff : run failures from previous test before running other test cases

For other options, see python -m pytest -h

Submitting Exercises

Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/sum-of-multiples directory.

You can find your Exercism workspace by running exercism debug and looking for the line that starts with Workspace.

For more detailed information about running tests, code style and linting, please see the help page.

Source

A variation on Problem 1 at Project Euler http://projecteuler.net/problem=1

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

sum_of_multiples_test.py

"""
You can make the following assumptions about the inputs to the
'sum_of_multiples' function:
    * All input numbers are non-negative 'int's, i.e. natural numbers
      including zero.
    * A list of factors must be given, and its elements are unique
      and sorted in ascending order.
"""

import unittest

from sum_of_multiples import sum_of_multiples


# Tests adapted from `problem-specifications//canonical-data.json` @ v1.2.0

class SumOfMultiplesTest(unittest.TestCase):
    def test_multiples_of_3_or_5_up_to_1(self):
        self.assertEqual(sum_of_multiples(1, [3, 5]), 0)

    def test_multiples_of_3_or_5_up_to_4(self):
        self.assertEqual(sum_of_multiples(4, [3, 5]), 3)

    def test_multiples_of_3_up_to_7(self):
        self.assertEqual(sum_of_multiples(7, [3]), 9)

    def test_multiples_of_3_or_5_up_to_10(self):
        self.assertEqual(sum_of_multiples(10, [3, 5]), 23)

    def test_multiples_of_3_or_5_up_to_100(self):
        self.assertEqual(sum_of_multiples(100, [3, 5]), 2318)

    def test_multiples_of_3_or_5_up_to_1000(self):
        self.assertEqual(sum_of_multiples(1000, [3, 5]), 233168)

    def test_multiples_of_7_13_or_17_up_to_20(self):
        self.assertEqual(sum_of_multiples(20, [7, 13, 17]), 51)

    def test_multiples_of_4_or_6_up_to_15(self):
        self.assertEqual(sum_of_multiples(15, [4, 6]), 30)

    def test_multiples_of_5_6_or_8_up_to_150(self):
        self.assertEqual(sum_of_multiples(150, [5, 6, 8]), 4419)

    def test_multiples_of_5_or_25_up_to_51(self):
        self.assertEqual(sum_of_multiples(51, [5, 25]), 275)

    def test_multiples_of_43_or_47_up_to_10000(self):
        self.assertEqual(sum_of_multiples(10000, [43, 47]), 2203160)

    def test_multiples_of_1_up_to_100(self):
        self.assertEqual(sum_of_multiples(100, [1]), 4950)

    def test_multiples_of_an_empty_list_up_to_10000(self):
        self.assertEqual(sum_of_multiples(10000, []), 0)


if __name__ == '__main__':
    unittest.main()
# lazy brute-force solution

def get_multiples_up_to(n, limit):
    multiples = []
    num = n
    while num < limit:
        multiples.append(num)
        num += n
    return multiples

def sum_of_multiples(limit, multiples):
    to_sum = set()
    for multiple in multiples:
        to_sum.update(set(get_multiples_up_to(multiple, limit)))

    return sum(to_sum)

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?