背包问题的haskell解法

-- file: knapsack1.hs

maxVal [] [] _ = 0

maxVal (w:ws) (v:vs) aW =
if w > aW
then
without_it
else
max without_it (with_it+v)
where
without_it = maxVal ws vs aW
with_it = maxVal ws vs (aW-w)

weights = [1, 5, 3, 4]
vals = [15, 10, 9, 5]

evalue = maxVal weights vals 8

-- file: knapsack2.hs

maxVal [] [] _ = (0, 0)

maxVal (w:ws) (v:vs) aW =
if w > aW
then
(without_it, nc1+1)
else
(max without_it (with_it+v), nc1+nc2+1)
where
(without_it, nc1) = maxVal ws vs aW
(with_it, nc2) = maxVal ws vs (aW-w)

weights = [1, 5, 3, 4]
vals = [15, 10, 9, 5]

evalue = maxVal weights vals 8

-- file: knapsack3.hs

maxVal [] [] _ = (0, 0, [])

maxVal (w:ws) (v:vs) aW =
if w > aW then
(without_it, nc1+1, 0:xs1)
else if without_it > with_it then
(without_it, nc1+nc2+1, 0:xs1)
else
(with_it, nc1+nc2+1, 1:xs2)
where
(without_it, nc1, xs1) = maxVal ws vs aW
(with_it', nc2, xs2) = maxVal ws vs (aW-w)
with_it = with_it' + v

weights = [1, 5, 3, 4]
vals = [15, 10, 9, 5]

evalue = maxVal weights vals 8