On Mon, Jun 01, 2009 at 10:55:30AM -0400, Thomas Friedrich wrote:
Ok, I don't really think I know what you are planing to do. Say I'd like to have 175 € form an ATM and [200, 100, 50, 20, 10,5] is the list of bills that can be used to cash this money. Do you what to produce a list like [0,1,1,1,0,1]? Telling you that you have to take one 100€ bill, one 50€ bill, etc...
Then I would do it the following:
cashout :: (Integral a) => a -> [a] -> [a] cashout 0 _ = [] cashout _ [] = error "*** in cashout: Not cashable." cashout tocash (b:bs) = fst r : cashout (snd r) bs where r = tocash `divMod` b
prop_cashout tocash bills = tocash == sum (zipWith (*) (cashout tocash bills) bills)
Hence,
cashout 175 [200,100,50,20,10,5] == [0,1,1,1,0,1]
But maybe you want something different.
It sounded to me a little different: like if you withdraw 200 €, you don't just want a 200 € bill, you want some small bills too: so you would get two 5s, two 10s, a 20, a 50, and a 100. -Brent