day 15

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

day15.hs

@@ -0,0 +1,86 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ViewPatterns #-}
+
+import Data.List (nub, sort)
+import Data.Text (Text)
+import qualified Data.Text as T (lines, null, split)
+import qualified Data.Text.Read as T (decimal, signed)
+import Lib (readFile')
+
+-- broh this is so slow ~ 20s, -O2 is less than 2s though???????
+-- will optimize this later, along with last 10 days *sigh*
+
+main :: IO ()
+main = do
+  input <- map parse . T.lines <$> readFile' "day15.in"
+  putStr "Q1: "
+  print $ q1 input 2000000
+  putStr "Q2: "
+  print $ q2 input input 0 4000000
+
+type Entity = (Int, Int, Int, Int, Int)
+
+q1 :: [Entity] -> Int -> Int
+q1 input n = mergeRanges getRanges
+  where
+    mergeRanges :: [(Int, Int)] -> Int
+    mergeRanges [(x0, x1)] = x1 - x0 + 1
+    mergeRanges ((x0, x1) : (x2, x3) : xs)
+      | x2 - x1 < 2 = mergeRanges $ (x0, max x1 x3) : xs
+      | otherwise = x1 - x0 + 1 + mergeRanges ((x2, x3) : xs)
+
+    getRanges :: [(Int, Int)]
+    getRanges =
+      sort $
+        foldr
+          ( \(x, y, r, a, b) xs -> case r - abs (n - y) of
+              dx
+                | dx < 0 -> xs
+                | n == b -> (x - dx, a - 1) : (a + 1, x + dx) : xs
+                | otherwise -> (x - dx, x + dx) : xs
+          )
+          []
+          input
+
+q2 :: [Entity] -> [Entity] -> Int -> Int -> Int
+q2 input@((x, y, succ -> e, a, b) : xs) all mn mx =
+  let (x', y') = dirs [(-1, -1), (1, -1), (1, 1), (-1, 1)]
+   in if (x', y') == (mn - 1, mn - 1) then q2 xs all mn mx else x' * mx + y'
+  where
+    dirs :: [(Int, Int)] -> (Int, Int)
+    dirs [] = (mn - 1, mn - 1)
+    dirs ((dx, dy) : ds) =
+      let b = border (dx, dy) (if dx * dy > 0 then [0 .. e - 1] else [e, e - 1 .. 1])
+       in if b == (mn - 1, mn - 1) then dirs ds else b
+
+    border :: (Int, Int) -> [Int] -> (Int, Int)
+    border _ [] = (mn - 1, mn - 1)
+    border (dx, dy) (b : bs) =
+      let (x', y') = (x + dx * b, y + dy * (e - b))
+       in if not (contains (x', y') all) && x' >= mn && x' <= mx && y' >= mn && y' <= mx
+            then (x', y')
+            else border (dx, dy) bs
+
+    contains :: (Int, Int) -> [Entity] -> Bool
+    contains (a', b') = any (\(x, y, r, a, b) -> r >= abs (b' - y) + abs (a' - x))
+
+parse :: Text -> Entity
+parse =
+  ( \[ "Sensor",
+       "at",
+       "x",
+       T.signed T.decimal -> Right (x, ""),
+       "y",
+       T.signed T.decimal -> Right (y, ""),
+       "closest",
+       "beacon",
+       "is",
+       "at",
+       "x",
+       T.signed T.decimal -> Right (a, ""),
+       "y",
+       T.signed T.decimal -> Right (b, "")
+       ] -> (x, y, abs (b - y) + abs (a - x), a, b)
+  )
+    . filter (not . T.null)
+    . T.split (`elem` (":=, " :: [Char]))