Pythagorean triples: Difference between revisions

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@@ Line 1,706: / Line 1,706: @@
 Recursive primitive generation:
 <lang haskell>triangles :: Int -> [[Int]]
-triangles max_peri | max_peri < 12 = []
+triangles max_peri
+  | max_peri < 12 = []
-           | otherwise = concat tiers where
+  | otherwise = concat tiers
-    tiers = takeWhile (not.null) $ iterate tier [[3,4,5]]
+  where
-    tier = concatMap (filter ((<=max_peri).sum).tmul)
+    tiers = takeWhile (not . null) $ iterate tier [[3, 4, 5]]
-    tmul t = map (map (sum . zipWith (*) t))
+    tier = concatMap (filter ((<= max_peri) . sum) . tmul)
-        [[[ 1,-2,2],[ 2,-1,2],[ 2,-2,3]],
+    tmul t =
-         [[ 1, 2,2],[ 2, 1,2],[ 2, 2,3]],
+      map
-         [[-1, 2,2],[-2, 1,2],[-2, 2,3]]]
+        (map (sum . zipWith (*) t))
+        [ [[1, -2, 2], [2, -1, 2], [2, -2, 3]]
+        , [[1, 2, 2], [2, 1, 2], [2, 2, 3]]
+        , [[-1, 2, 2], [-2, 1, 2], [-2, 2, 3]]
+        ]
-triangle_count max_p = (length t, sum $ map ((max_p `div`).sum) t)
+triangleCount max_p = (length t, sum $ map ((max_p `div`) . sum) t)
-    where t = triangles max_p
+  where
+    t = triangles max_p
-main = mapM_ putStrLn $
+main :: IO ()
+main =
-    map (\n -> show n ++ " " ++ show (triangle_count n)) $ map (10^) [1..]</lang>
+  mapM_
+    ((putStrLn . (\n -> show n ++ " " ++ show (triangleCount n))) . (10 ^))
+    [1 .. 7]</lang>
 {{out}}
-<pre>
+<pre>10 (0,0)
-(0,0)
 (7,17)
 (70,325)
@@ Line 1,728: / Line 1,736: @@
 (7026,64741)
 1000000 (70229,808950)
-10000000 (702309,9706567)
+10000000 (702309,9706567)</pre>
-...
-</pre>
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