September 2017 Update

Task/Zig-zag-matrix/Haskell/zig-zag-matrix-3.hs

@@ -0,0 +1,37 @@
+import Data.List (mapAccumL)
+import Data.Text (justifyRight, pack, unpack)
+
+zigZag :: Int -> [[Int]]
+zigZag n = horizontals n (diagonals n)
+  where
+
+    diagonals :: Int -> [[Int]]
+    diagonals n =
+      snd $
+      mapAccumL
+        (\xs h ->
+            let (grp, rst) = splitAt h xs
+            in ( rst
+               , (if mod h 2 /= 0
+                    then reverse
+                    else id)
+                   grp))
+        [0 .. (n * n) - 1]
+        (slope ++ [n] ++ reverse slope)
+      where
+        slope = [1 .. n - 1]
+
+    horizontals :: Int -> [[Int]] -> [[Int]]
+    horizontals n xss =
+      if not (null xss)
+        then let (edge, rst) = splitAt n xss
+             in (head <$> edge) :
+                horizontals n (dropWhile null (tail <$> edge) ++ rst)
+        else []
+
+main :: IO ()
+main =
+  putStrLn $
+  unlines $
+  (concat . (unpack <$>)) . ((justifyRight 3 ' ' . pack . show) <$>) <$>
+  zigZag 5