Python: book_store

python/book-store/.exercism/metadata.json

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+{"track":"python","exercise":"book-store","id":"cef3e9ecc90a4fcc9e92b878f280657a","url":"https://exercism.io/my/solutions/cef3e9ecc90a4fcc9e92b878f280657a","handle":"DmitryKokorin","is_requester":true,"auto_approve":false}

python/book-store/README.md

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+# Book Store
+
+To try and encourage more sales of different books from a popular 5 book
+series, a bookshop has decided to offer discounts on multiple book purchases.
+
+One copy of any of the five books costs $8.
+
+If, however, you buy two different books, you get a 5%
+discount on those two books.
+
+If you buy 3 different books, you get a 10% discount.
+
+If you buy 4 different books, you get a 20% discount.
+
+If you buy all 5, you get a 25% discount.
+
+Note: that if you buy four books, of which 3 are
+different titles, you get a 10% discount on the 3 that
+form part of a set, but the fourth book still costs $8.
+
+Your mission is to write a piece of code to calculate the
+price of any conceivable shopping basket (containing only
+books of the same series), giving as big a discount as
+possible.
+
+For example, how much does this basket of books cost?
+
+- 2 copies of the first book
+- 2 copies of the second book
+- 2 copies of the third book
+- 1 copy of the fourth book
+- 1 copy of the fifth book
+
+One way of grouping these 8 books is:
+
+- 1 group of 5 --> 25% discount (1st,2nd,3rd,4th,5th)
+- +1 group of 3 --> 10% discount (1st,2nd,3rd)
+
+This would give a total of:
+
+- 5 books at a 25% discount
+- +3 books at a 10% discount
+
+Resulting in:
+
+- 5 x (8 - 2.00) == 5 x 6.00 == $30.00
+- +3 x (8 - 0.80) == 3 x 7.20 == $21.60
+
+For a total of $51.60
+
+However, a different way to group these 8 books is:
+
+- 1 group of 4 books --> 20% discount  (1st,2nd,3rd,4th)
+- +1 group of 4 books --> 20% discount  (1st,2nd,3rd,5th)
+
+This would give a total of:
+
+- 4 books at a 20% discount
+- +4 books at a 20% discount
+
+Resulting in:
+
+- 4 x (8 - 1.60) == 4 x 6.40 == $25.60
+- +4 x (8 - 1.60) == 4 x 6.40 == $25.60
+
+For a total of $51.20
+
+And $51.20 is the price with the biggest discount.
+
+
+## Exception messages
+
+Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
+indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
+every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
+a message.
+
+To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
+`raise Exception`, you should write:
+
+```python
+raise Exception("Meaningful message indicating the source of the error")
+```
+
+## Running the tests
+
+To run the tests, run `pytest book_store_test.py`
+
+Alternatively, you can tell Python to run the pytest module:
+`python -m pytest book_store_test.py`
+
+### Common `pytest` options
+
+- `-v` : enable verbose output
+- `-x` : stop running tests on first failure
+- `--ff` : run failures from previous test before running other test cases
+
+For other options, see `python -m pytest -h`
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/book-store` 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 [Running the Tests](http://exercism.io/tracks/python/tests).
+
+## Source
+
+Inspired by the harry potter kata from Cyber-Dojo. [http://cyber-dojo.org](http://cyber-dojo.org)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

python/book-store/book_store.py

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+from collections import Counter
+from itertools import combinations
+
+DISCOUNTS = [0, 0, 5, 10, 20, 25]
+BOOK_COST = 8
+
+
+def get_discount(counter):
+
+    xs = sorted([i for i in counter if i != 0], reverse=True)
+
+    if not xs:
+        return 0
+
+    discount = 0
+
+    for group_size in range(1, len(xs) + 1):
+        for xs1 in combinations(xs, len(xs)):
+            xs1 = [item - 1 if index < group_size else item
+                   for index, item in enumerate(xs1)]
+            curr_discount = (
+                DISCOUNTS[group_size]*group_size + get_discount(xs1)
+            )
+            if curr_discount > discount:
+                discount = curr_discount
+
+    return discount
+
+
+def total(basket):
+
+    return BOOK_COST*(len(basket)*100
+                      - get_discount(Counter(basket).values()))

python/book-store/book_store_test.py

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+import unittest
+
+from book_store import total
+
+# Tests adapted from `problem-specifications//canonical-data.json`
+
+
+class BookStoreTest(unittest.TestCase):
+    def test_only_a_single_book(self):
+        basket = [1]
+        self.assertEqual(total(basket), 800)
+
+    def test_two_of_the_same_book(self):
+        basket = [2, 2]
+        self.assertEqual(total(basket), 1600)
+
+    def test_empty_basket(self):
+        basket = []
+        self.assertEqual(total(basket), 0)
+
+    def test_two_different_books(self):
+        basket = [1, 2]
+        self.assertEqual(total(basket), 1520)
+
+    def test_three_different_books(self):
+        basket = [1, 2, 3]
+        self.assertEqual(total(basket), 2160)
+
+    def test_four_different_books(self):
+        basket = [1, 2, 3, 4]
+        self.assertEqual(total(basket), 2560)
+
+    def test_five_different_books(self):
+        basket = [1, 2, 3, 4, 5]
+        self.assertEqual(total(basket), 3000)
+
+    def test_two_groups_of_four_is_cheaper_than_group_of_five_plus_group_of_three(self):
+        basket = [1, 1, 2, 2, 3, 3, 4, 5]
+        self.assertEqual(total(basket), 5120)
+
+    def test_two_groups_of_four_is_cheaper_than_groups_of_five_and_three(self):
+        basket = [1, 1, 2, 3, 4, 4, 5, 5]
+        self.assertEqual(total(basket), 5120)
+
+    def test_group_of_four_plus_group_of_two_is_cheaper_than_two_groups_of_three(self):
+        basket = [1, 1, 2, 2, 3, 4]
+        self.assertEqual(total(basket), 4080)
+
+    def test_two_each_of_first_4_books_and_1_copy_each_of_rest(self):
+        basket = [1, 1, 2, 2, 3, 3, 4, 4, 5]
+        self.assertEqual(total(basket), 5560)
+
+    def test_two_copies_of_each_book(self):
+        basket = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5]
+        self.assertEqual(total(basket), 6000)
+
+    def test_three_copies_of_first_book_and_2_each_of_remaining(self):
+        basket = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 1]
+        self.assertEqual(total(basket), 6800)
+
+    def test_three_each_of_first_2_books_and_2_each_of_remaining_books(self):
+        basket = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 1, 2]
+        self.assertEqual(total(basket), 7520)
+
+    def test_four_groups_of_four_are_cheaper_than_two_groups_each_of_five_and_three(
+        self
+    ):
+        basket = [1, 1, 2, 2, 3, 3, 4, 5, 1, 1, 2, 2, 3, 3, 4, 5]
+        self.assertEqual(total(basket), 10240)
+
+    # Additional tests for this track
+
+    def test_two_groups_of_four_and_a_group_of_five(self):
+        basket = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 5, 5]
+        self.assertEqual(total(basket), 8120)
+
+    def test_shuffled_book_order(self):
+        basket = [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3]
+        self.assertEqual(total(basket), 8120)
+
+
+if __name__ == "__main__":
+    unittest.main()