From 71824cf748b1deb97422f80c2866a0283d40c373 Mon Sep 17 00:00:00 2001 From: Correl Roush Date: Tue, 11 Oct 2011 23:20:31 -0400 Subject: [PATCH] Haskell 009 documented and using a data structure --- haskell/e009.hs | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/haskell/e009.hs b/haskell/e009.hs index 4e6e157..7d8af99 100644 --- a/haskell/e009.hs +++ b/haskell/e009.hs @@ -10,18 +10,29 @@ Find the product abc. import Text.Printf +-- |A triangle consisting of three integral sides +data Triangle = Triangle Int Int Int + +-- |Return the product of the sides of the first triangle having the sum of the sides 'sum' +triplet :: Int -> Int triplet sum = do let cs = reverse (takeWhile (<= sum - 3) [3,5..]) - let tri = head (concat (map (\x -> diffs sum x) cs)) - let (a, b, c) = tri + let tri = head (concat (map (\x -> right_triangles sum x) cs)) + let (Triangle a b c) = tri a * b * c -diffs sum c = do + +-- |Find all right triangles having sum of sides 'sum' and side c length of 'c' +right_triangles :: Int -> Int -> [Triangle] +right_triangles sum c = do let diff = sum - c let range = [1..(floor ((fromIntegral diff) / 2)) + 1] - let triangles = filter is_triangle (map (\x -> (x, diff - x, c)) range) + let triangles = filter is_right_triangle (map (\x -> Triangle x (diff - x) c) range) triangles -is_triangle (a, b, c) = + +-- |Return whether the provided triangle is a right triangle using the pythagorean theorem +is_right_triangle :: Triangle -> Bool +is_right_triangle (Triangle a b c) = a^2 + b^2 == c^2 main = do - printf "Pythagorean triplet product having a + b + c = 1000: %d\n" (triplet 1000 :: Integer) + printf "Pythagorean triplet product having a + b + c = 1000: %d\n" (triplet 1000 :: Int)