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module Ch2 where
minmax :: Ord a => [a] -> (Maybe a,Maybe a)
minmax [] = (Nothing,Nothing)
minmax [x] = (Just x,Just x)
minmax (x:y:xs)
| x < y = let (minVal,maxVal) = minmax (x:xs)
in (minVal, max (Just y) maxVal)
| otherwise = let (minVal,maxVal) = minmax (y:xs)
in (minVal, max (Just x) maxVal)
maxDistance :: (Ord a, Num a) => [a] -> [a] -> Maybe a
maxDistance xs ys = liftA2 max diff1 diff2
where
(min_xs,max_xs) = minmax xs
(min_ys,max_ys) = minmax ys
diff1 = liftA2 (-) max_xs min_ys
diff2 = liftA2 (-) max_ys min_xs
main :: IO ()
main = do
print $ maxDistance [4,5,7] [9,1,3,4]
print $ maxDistance [2,3,5,4] [3,2,5,5,8,7]
print $ maxDistance [2,1,11,3] [2,5,10,2]
print $ maxDistance [1,2,3] [3,2,1]
print $ maxDistance [1,0,2,3] [5,0]
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