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Haskell 009 documented and using a data structure

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Correl Roush 2011-10-11 23:20:31 -04:00
parent c0ab42edf9
commit 71824cf748
1 changed files with 17 additions and 6 deletions
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haskell/e009.hs
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@ -10,18 +10,29 @@ Find the product abc.
import Text.Printf 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 triplet sum = do
let cs = reverse (takeWhile (<= sum - 3) [3,5..]) let cs = reverse (takeWhile (<= sum - 3) [3,5..])
let tri = head (concat (map (\x -> diffs sum x) cs)) let tri = head (concat (map (\x -> right_triangles sum x) cs))
let (a, b, c) = tri let (Triangle a b c) = tri
a * b * c 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 diff = sum - c
let range = [1..(floor ((fromIntegral diff) / 2)) + 1] 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 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 a^2 + b^2 == c^2
main = do 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)