Created
June 10, 2015 12:36
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data Section = Section { getA :: Int, getB :: Int, getC :: Int } | |
deriving (Show) | |
type RoadSystem = [Section] | |
heathrowToLondon :: RoadSystem | |
heathrowToLondon = [ Section 50 10 30 | |
, Section 5 90 20 | |
, Section 40 2 25 | |
, Section 10 8 0 | |
] | |
data Label = A | B | C deriving (Show) | |
type Path = [(Label, Int)] | |
roadStep :: (Path, Path) -> Section -> (Path, Path) | |
roadStep (pathA, pathB) (Section a b c) = | |
let timeA = sum (map snd pathA) | |
timeB = sum (map snd pathB) | |
forwardTimeToA = timeA + a | |
crossTimeToA = timeB + b + c | |
forwardTimeToB = timeB + b | |
crossTimeToB = timeA + a + c | |
newPathToA = if forwardTimeToA <= crossTimeToA | |
then (A, a):pathA | |
else (C, c):(B, b):pathB | |
newPathToB = if forwardTimeToB <= crossTimeToB | |
then (B, b):pathB | |
else (C, c):(A, a):pathA | |
in (newPathToA, newPathToB) | |
optimalPath :: RoadSystem -> Path | |
optimalPath roadSystem = | |
let (bestAPath, bestBPath) = foldl roadStep ([], []) roadSystem | |
in if sum (map snd bestAPath) <= sum (map snd bestBPath) | |
then reverse bestAPath | |
else reverse bestBPath | |
main = do | |
print $ roadStep ([], []) (head heathrowToLondon) | |
print $ optimalPath heathrowToLondon |
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