Instructions
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 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 (1st, 2nd,3rd, 4th, 5th)
- 1 group of 3 (1st, 2nd, 3rd)
This would give a total of:
- 5 books at a 25% discount
- 3 books at a 10% discount
Resulting in:
- 5 × (100% - 25%) × $8 = 5 × $6.00 = $30.00, plus
- 3 × (100% - 10%) × $8 = 3 × $7.20 = $21.60
Which equals $51.60.
However, a different way to group these 8 books is:
- 1 group of 4 books (1st, 2nd, 3rd, 4th)
- 1 group of 4 books (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 × (100% - 20%) × $8 = 4 × $6.40 = $25.60, plus
- 4 × (100% - 20%) × $8 = 4 × $6.40 = $25.60
Which equals $51.20.
And $51.20 is the price with the biggest discount.
WebAssembly-specific Notes
The function signature for the WebAssembly export total is as follows:
(func (export "total")
(param $basketOffset i32)
(param $basketLength i32)
(result i32)
)
The two parameters $basketOffset and $basketLength express the base offset and length of an array of 32-bit integers. The length parameter is sized in number of elements in the array, not bytes. Prior to calling this function, the caller writes this array into the WebAssembly linear memory beginning at offset $basketOffset. WebAssembly linear memory is always expressed in little-endian.
For example, the caller would encode the basket [1,2] as the following eight byte sequence.
| 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 |
| --- basket[0] --- | --- basket[1] --- |
,0x01,0x00,0x00,0x00,0x02,0x00,0x00,0x00,
