1 files changed, 53 insertions, 0 deletions
diff --git a/3-kyu/make-a-spiral.hs b/3-kyu/make-a-spiral.hs
new file mode 100644
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+++ b/3-kyu/make-a-spiral.hs
@@ -0,0 +1,53 @@
+-- https://www.codewars.com/kata/534e01fbbb17187c7e0000c6
+module Spiral where
+
+setRow :: Int -> (Int, Int) -> [[Int]] -> [[Int]]
+setRow r (from, to) mat = take r mat ++ [set oldRow] ++ drop (r+1) mat
+  where
+    oldRow = head $ drop r mat
+    set row = take from row ++ take (to - from + 1) (repeat 1) ++ drop (to+1) row
+
+setCol :: Int -> (Int, Int) -> [[Int]] -> [[Int]]
+setCol c (from, to) mat =
+  take from mat
+  ++ map (setNth c) (drop from $ take (to+1) mat)
+  ++ drop (to+1) mat
+    where
+      setNth n row = take n row ++ [1] ++ drop (n+1) row
+
+emptySquare :: Int -> [[Int]]
+emptySquare n = take n $ repeat $ take n $ repeat 0
+
+data Direction = DRight | DLeft | DDown | DUp
+
+spiralize :: Int -> [[Int]]
+spiralize n = go (emptySquare n) (0,0) [n-1,n-1,0] n DRight
+  where
+    go mat (x,y) limit prevDelta DRight =
+      if x >= head limit || prevDelta < 2 then mat
+      else go (setRow y (x,head limit) mat)
+              (head limit, y)
+              (tail limit ++ [y+2])
+              (head limit - x)
+              DDown
+    go mat (x,y) limit prevDelta DDown =
+      if y >= head limit || prevDelta < 2 then mat
+      else go (setCol x (y, head limit) mat)
+              (x, head limit)
+              (tail limit ++ [x-2])
+              (head limit - y)
+              DLeft
+    go mat (x,y) limit prevDelta DLeft =
+      if x <= head limit || prevDelta < 2 then mat
+      else go (setRow y (head limit, x) mat)
+              (head limit, y)
+              (tail limit ++ [y-2])
+              (x - head limit)
+              DUp
+    go mat (x,y) limit prevDelta DUp =
+      if y <= head limit || prevDelta < 2 then mat
+      else go (setCol x (head limit, y) mat)
+              (x, head limit)
+              (tail limit ++ [x+2])
+              (y - head limit)
+              DRight