Add 2020 day 11

haskellAoC/src/Y2020/Day11.hs

@@ -0,0 +1,65 @@
+module Y2020.Day11 (y20day11) where
+
+import Data.Matrix
+
+type Setting = Matrix Char
+
+empty :: Char
+empty = 'L'
+
+occupied :: Char
+occupied = '#'
+
+directions :: [(Int, Int)]
+directions = [(-1, -1), (0, -1), (1, -1),
+              (-1,  0),          (1,  0),
+              (-1,  1), (0,  1), (1,  1)]
+
+countOccupiedSeatsP1 :: Setting -> (Int, Int) -> Int
+countOccupiedSeatsP1 old (x, y) = length $ filter (== occupied) $ map ((!) old) $ filter validPos $ adjacentSeats
+  where adjacentSeats = map (\(dx, dy) -> (x + dx, y + dy)) $ directions
+        validPos (x', y') = x' >= 1 && y' >= 1 && x' <= (ncols old) && y' <= (nrows old)
+
+countOccupiedSeatsP2 :: Setting -> (Int, Int) -> Int
+countOccupiedSeatsP2 old p = length $ filter (== occupied) $ map (getFirstSeat p) $ directions
+  where validPos (x, y) = x >= 1 && y >= 1 && x <= (ncols old) && y <= (nrows old)
+        getFirstSeat (x, y) (dx, dy)
+          | not $ validPos (x', y') = '.'
+          | inSight == '.' = getFirstSeat (x', y') (dx, dy)
+          | otherwise = inSight
+          where x' = x + dx
+                y' = y + dy
+                inSight = old ! (x', y')
+
+generatorFunc :: Int -> Setting -> (Int, Int) -> Char
+generatorFunc part old p
+  | oldPos == empty && (occupiedSeats part) == 0 = occupied
+  | oldPos == occupied && (occupiedSeats part) >= (occupiedThreshold part) = empty
+  | otherwise = oldPos
+  where oldPos = old ! p
+        occupiedSeats 1 = countOccupiedSeatsP1 old p
+        occupiedSeats 2 = countOccupiedSeatsP2 old p
+        occupiedThreshold 1 = 4
+        occupiedThreshold 2 = 5
+
+nextSetting :: Int -> Setting -> Setting
+nextSetting part setting = matrix cols rows $ generatorFunc part setting
+  where cols = ncols setting
+        rows = nrows setting
+
+hasChanged :: Setting -> Setting -> Bool
+hasChanged previous current = previous /= current
+
+getStabilizedSetting :: Int -> Setting -> Setting
+getStabilizedSetting part setting
+  | nextHasChanged == True = getStabilizedSetting part next
+  | otherwise = setting
+  where next = nextSetting part setting
+        nextHasChanged = hasChanged setting next
+
+y20day11 :: [String] -> (String, String)
+y20day11 input = (part1, part2)
+  where part1 = show $ countOccupied $ getStabilizedSetting 1 input'
+        part2 = show $ countOccupied $ getStabilizedSetting 2 input'
+        input' = fromLists input
+        countOccupied mat = length $ filter (== occupied) $ toList mat

haskellAoC/src/Y2020/Days.hs

@@ -10,6 +10,7 @@ import Y2020.Day07
 import Y2020.Day08
 import Y2020.Day09
 import Y2020.Day10
+import Y2020.Day11
 
 year2020 :: String -> [String] -> (String, String)
 year2020 "01" = y20day01
@@ -22,3 +23,4 @@ year2020 "07" = y20day07
 year2020 "08" = y20day08
 year2020 "09" = y20day09
 year2020 "10" = y20day10
+year2020 "11" = y20day11