Daniel Fischer wrote:
If f has the appropriate type and the base case is f 0 = 0,
module Memo where
import Data.Array
f :: (Integral a, Ord a, Ix a) => a -> a
f n = memo ! n
where
memo = array (0,n) $ (0,0) :
[(i, max i (memo!(i `quot` 2) + memo!(i `quot` 3)
+ memo!(i `quot` 4))) | i <- [1 .. n]]
is wasteful regarding space, but it calculates only the needed values and
very simple.
Can someone explain to a beginner like me why this calculates only the
needed values? The list comprehension draws from 1..n so I don't
understand why all those values wouldn't be computed.
Thanks
Mike
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