8-2

1 files changed, 78 insertions, 0 deletions

diff --git a/8-2.hs b/8-2.hs
new file mode 100644
index 0000000..c573a51
--- /dev/null
+++ b/8-2.hs
@@ -0,0 +1,78 @@
+import Data.List (nub)
+import Data.Maybe (mapMaybe)
+
+pairs :: [a] -> [(a,a)]
+pairs = go []
+  where
+    go :: [(a,a)] -> [a] -> [(a,a)]
+    go res []     = res
+    go res (x:xs) = go (map (x,) xs ++ res) xs
+
+antinodes :: (Int,Int) -> (Int,Int) -> (Int,Int) -> [(Int,Int)]
+antinodes (w,h) (x1,y1) (x2,y2) =
+  [ (x,y) | x <- [0..w-1], y <- [0..h-1], f x y ]
+  where
+    f :: Int -> Int -> Bool
+    f x y = fromIntegral y == m * fromIntegral (x - x1) + fromIntegral y1
+
+    m :: Double
+    m = let x1' = fromIntegral x1
+            x2' = fromIntegral x2
+            y1' = fromIntegral y1
+            y2' = fromIntegral y2
+        in (y2' - y1') / (x2' - x1')
+
+separate :: [(Char,(Int,Int))] -> [[(Int,Int)]]
+separate = map snd . go []
+  where
+    go :: [(Char,[(Int,Int)])]
+       -> [(Char,(Int,Int))]
+       -> [(Char,[(Int,Int)])]
+    go res [] = res
+    go res (x:xs) = go (f res x) xs
+
+    f :: [(Char,[(Int,Int)])]
+      -> (Char,(Int,Int))
+      -> [(Char,[(Int,Int)])]
+    f xs (c,pos) = case lookup c xs of
+      Nothing   -> (c,[pos]) : xs
+      Just poss -> (c,pos:poss) : rm c xs
+
+rm :: Eq a => a -> [(a,b)] -> [(a,b)]
+rm = go []
+  where
+    go :: Eq a => [(a,b)] -> a -> [(a,b)] -> [(a,b)]
+    go res _ [] = res
+    go res x (a@(p,_):xs) | p == x = go res x xs
+                          | otherwise = go (a:res) x xs
+
+parse :: String -> [(Char,(Int,Int))]
+parse s = mapMaybe lift' . flip zip coords . concatMap (map f) . lines $ s
+  where
+    f :: Char -> Maybe Char
+    f '.' = Nothing
+    f x   = Just x
+
+    coords :: [(Int,Int)]
+    coords = let w = length . head $ lines s
+                 h = length $ lines s
+             in [ (x,y) | x <- [0..w-1], y <- [0..h-1] ]
+
+    lift' :: (Maybe a,b) -> Maybe (a,b)
+    lift' (Just p,q)  = Just (p,q)
+    lift' (Nothing,_) = Nothing
+
+doStuff :: Int -> Int -> String -> Int
+doStuff w h = length
+  . nub
+  . concatMap (concatMap (uncurry (antinodes (w,h))) . pairs)
+  . separate
+  . parse
+
+main :: IO ()
+main = do
+  s <- getContents
+  let ls = lines s
+  let w = length . head $ ls
+  let h = length ls
+  print $ doStuff w h s