1 files changed, 80 insertions, 0 deletions
diff --git a/3-kyu/sudoku.hs b/3-kyu/sudoku.hs
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+++ b/3-kyu/sudoku.hs
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+-- https://www.codewars.com/kata/5296bc77afba8baa690002d7
+module Sudoku where
+
+import Data.List (find, transpose)
+
+sudoku :: [[Int]] -> [[Int]]
+sudoku input = stripMaybe $ fmap (chunksOf 9) $ solveSudoku $ foldl1 (++) $ input where
+  stripMaybe Nothing = []
+  stripMaybe (Just x) = x
+  
+
+chunksOf :: Int -> [a] -> [[a]]
+chunksOf n lst = go lst [] where
+  go [] ret = reverse ret
+  go rem ret = go (drop n rem) ((take n rem):ret)
+
+type ListZipper a = ([a], [a])
+
+moveForward :: ListZipper a -> Maybe (ListZipper a)
+moveForward (_, []) = Nothing
+moveForward (before, (x:xs)) = Just ((x:before), xs)
+
+toList :: ListZipper a -> [a]
+toList (before, after) = reverse before ++ after
+
+fromList :: [a] -> ListZipper a
+fromList lst = ([], lst)
+
+zipperModify :: a -> ListZipper a -> Maybe (ListZipper a)
+zipperModify _ (b, []) = Nothing
+zipperModify new (before, (x:xs)) = Just (before, (new:xs))
+
+zipperView :: ListZipper a -> Maybe a
+zipperView (_, []) = Nothing
+zipperView (_, (x:_)) = Just x
+
+firstJust :: [Maybe a] -> Maybe a
+firstJust lst = getResult $ find isJust lst where
+    getResult (Just (Just x)) = Just x
+    getResult _ = Nothing
+
+
+isJust :: Maybe a -> Bool
+isJust (Just _) = True
+isJust Nothing  = False
+
+solveSudoku :: [Int] -> Maybe [Int]
+solveSudoku s = go $ fromList s where
+  go z =
+    if not $ maybeValidSudoku $ toList z then Nothing
+    else
+      if moveForward z == Nothing then
+          Just $ toList z
+      else
+        if zipperView z /= Just 0 then moveForward z >>= go
+        else
+          firstJust $ map tryWith [1,2,3,4,5,6,7,8,9] where
+           tryWith x = zipperModify x z >>= moveForward >>= go
+        
+maybeValidSudoku :: [Int] -> Bool
+maybeValidSudoku x = all validLine (rows x ++ cols x ++ blocks x) where
+  validLine line = all isUnique [1,2,3,4,5,6,7,8,9] where
+    isUnique x = (length $ filter (==x) line) <= 1
+
+rows :: [Int] -> [[Int]]
+rows lst = chunksOf 9 lst
+
+cols :: [Int] -> [[Int]]
+cols lst = transpose $ chunksOf 9 lst
+
+blocks :: [Int] -> [[Int]]
+blocks lst = map block ([(rows, cols) | rows <- ranges, cols <- ranges]) where
+  ranges = [(0,2), (3,5), (6,8)]
+  block ((startx, endx), (starty, endy)) =
+    foldl1 (++)
+    $ colsRange startx endx
+    $ rowsRange starty endy
+    $ chunksOf 9 lst where
+      rowsRange start end mat = drop start $ take (end+1) mat
+      colsRange start end mat = transpose $ drop start $ take (end+1) $ transpose mat