1 files changed, 29 insertions, 0 deletions
diff --git a/2021/5.hs b/2021/5.hs
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+++ b/2021/5.hs
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+{-# LANGUAGE TupleSections #-}
+module Main where
+
+import qualified Data.Array as A
+
+import Input
+
+
+main :: IO ()
+main = do
+    let parseLine s = let [a,_,b] = words s in (parsePt a, parsePt b)
+        parsePt s = let (a,_:b) = break (== ',') s in (read a, read b) :: (Int, Int)
+    inp <- map parseLine <$> getInput 5
+    let minmax = (,) <$> minimum <*> maximum
+        (minx, maxx) = minmax (concatMap (\((a,_),(b,_)) -> [a,b]) inp)
+        (miny, maxy) = minmax (concatMap (\((_,a),(_,b)) -> [a,b]) inp)
+    let enumLine diag ((x1,y1),(x2,y2))
+          | (diag && abs (x1 - x2) == abs (y1 - y2)) || x1 == x2 || y1 == y2
+          = let dx = signum (x2 - x1)
+                dy = signum (y2 - y1)
+            in [(x1 + i * dx, y1 + i * dy)
+               | i <- [0 .. max (abs (x2 - x1)) (abs (y2 - y1))]]
+          | otherwise = []
+        bd diag = A.accumArray (+) (0::Int) ((minx, miny), (maxx, maxy))
+                      [((x, y), 1)
+                      | line <- inp
+                      , (x, y) <- enumLine diag line]
+    print (length (filter (> 1) (A.elems (bd False))))
+    print (length (filter (> 1) (A.elems (bd True))))