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jdhuntington/project_euler_problem_45.hs

Created August 26, 2009 15:52
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project_euler_problem_45.hs
import Data.List
triangulate x = x * ( 1 + x ) / 2
pentagulate x = x * ( 3 * x - 1 ) / 2
hexagulate x = x * ( 2 * x - 1 )
triangles = [ triangulate x | x <- [1..] ]
pentagons = [ pentagulate x | x <- [1..] ]
memberOfIncreasingSequence x = (==x).head.dropWhile(<x)
isTriangle = flip memberOfIncreasingSequence triangles
isPentagon = flip memberOfIncreasingSequence pentagons
-- take 3 [ x | x <- [1..], isTriangle $ hexagulate x, isPentagon $ hexagulate x ]
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