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-- 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
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