Knight's tour: Difference between revisions

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@@ Line 4,086: / Line 4,086: @@
 =={{header|Haskell}}==
-<lang Haskell>{-# LANGUAGE TupleSections #-}
+<lang Haskell>import Data.Bifunctor (bimap)
+import Data.Char (chr, ord)
-import Data.List (minimumBy, (\\), intercalate, sort)
+import Data.List (intercalate, minimumBy, sort, (\\))
 import Data.Ord (comparing)
-import Data.Char (ord, chr)
+---------------------- KNIGHT'S TOUR ---------------------
-import Data.Bool (bool)
 type Square = (Int, Int)
@@ Line 4,100: / Line 4,100: @@
   | otherwise = knightTour $ newSquare : moves
   where
-    newSquare = minimumBy (comparing (length . findMoves)) possibilities
+    newSquare =
+      minimumBy
+        (comparing (length . findMoves))
+        possibilities
     possibilities = findMoves $ head moves
     findMoves = (\\ moves) . knightOptions
@@ Line 4,106: / Line 4,109: @@
 knightOptions :: Square -> [Square]
 knightOptions (x, y) =
-  knightMoves >>=
+  knightMoves >>= go . bimap (+ x) (+ y)
+  where
-  (\(i, j) ->
-      let a = x + i
+    go (a, b)
-          b = y + j
+      | onBoard a && onBoard b = [(a, b)]
+      | otherwise = []
-      in bool [] [(a, b)] (onBoard a && onBoard b))
 knightMoves :: [(Int, Int)]
-knightMoves =
+knightMoves = (deltas >>=) . go =<< deltas
+  where
-  let deltas = [id, negate] <*> [1, 2]
-  in deltas >>=
+    deltas = [id, negate] <*> [1, 2]
+    go i x
-     (\i -> deltas >>= (bool [] . return . (i, )) <*> ((abs i /=) . abs))
+      | abs i /= abs x = [(i, x)]
+      | otherwise = []
 onBoard :: Int -> Bool
 onBoard = (&&) . (0 <) <*> (9 >)
--- TEST ---------------------------------------------------
+--------------------------- TEST -------------------------
+startPoint :: String
 startPoint = "e5"
@@ Line 4,130: / Line 4,136: @@
 main =
   printTour $
+    algebraic
-  algebraic <$> knightTour [(\[x, y] -> (ord x - 96, ord y - 48)) startPoint]
+      <$> knightTour
+        [(\[x, y] -> (ord x - 96, ord y - 48)) startPoint]
   where
     printTour [] = return ()