Zig-zag matrix: Difference between revisions

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@@ Line 2,193: / Line 2,193: @@
 zigZag :: Int -> [[Int]]
-zigZag = horizontals <*> diagonals
+zigZag = go <*> diagonals
   where
-    diagonals n =
+    go _ [] = []
+    go n xss = (head <$> edge) : go n (dropWhile null (tail <$> edge) <> rst)
-      let slope = [1 .. n - 1]
-      in snd $
+      where
-         mapAccumL
+        (edge, rst) = splitAt n xss
-           (\xs h ->
+diagonals :: Int -> [[Int]]
-               let (grp, rst) = splitAt h xs
+diagonals n =
-               in (rst, bool id reverse (0 /= mod h 2) grp))
-           [0 .. (n * n) - 1]
+  snd $ mapAccumL go [0 .. (n * n) - 1] (slope <> [n] <> reverse slope)
+  where
-           (slope ++ [n] ++ reverse slope)
-    horizontals n xss
+    slope = [1 .. n - 1]
+    go xs h = (rst, bool id reverse (0 /= mod h 2) grp)
-      | null xss = []
-      | otherwise =
+      where
-        let (edge, rst) = splitAt n xss
+        (grp, rst) = splitAt h xs
-        in (head <$> edge) :
-           horizontals n (dropWhile null (tail <$> edge) ++ rst)
 main :: IO ()