Test Error in Exercise "Book Store"

[cmccandless]

The test "Basket_with_eight_books" tests for a sum value of "51.20", when the correct sum should be "51.60".

E.G: books=[1,1,2,2,3,3,4,5]
groups=[count(1,2,3,4,5),count(1,2,3)]=[5,3]
discount[5]=.75
discount[3]=.9
groups8=[40,24]
groups8discount=[40.75,24*.9]=[30,21.6]
total=30+21.6=51.60

This particular example also happens to be contained in the Readme for the exercise, but the arithmetic was done correctly there.

[robkeim]

@cmccandless are you talking about this readme?

If so, the Readme calls out two different groupings for the eights books, and you need to choose the cheaper one. If you're getting 51.60 it's probably because you're using a greedy algorithm and the greedy algorithm doesn't always work in this problem :)

[robkeim]

Copying the relevant part of the readme for your convenience:

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.

[cmccandless]

Ah, that's what I get for trying to code before coffee; I misunderstood that part of the readme. My mistake.