day11/python: optimizations

.gitignore

@@ -1 +1 @@
-example.txt
+example*

README.md

@@ -17,5 +17,6 @@ https://adventofcode.com/2020/
 | 9 |        |  `**`   |      |
 |10 |        |  `**`   |      |
 |11 |  `**`  |         |      |
+|13 |        |  `**`   |      |
 
 `test.sh` can be used to run all solutions and automatically compares them to (my) puzzle inputs and the expected outputs.

data/day13.expected

@@ -0,0 +1,2 @@
+2215
+1058443396696792

data/day13.input

@@ -0,0 +1,2 @@
+1005162
+19,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,823,x,x,x,x,x,x,x,23,x,x,x,x,x,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,443,x,x,x,x,x,37,x,x,x,x,x,x,13

day11/day11.py

@@ -57,20 +57,17 @@ class Layout:
         return len(new_tiles) != 0
 
     def _find_neighbour(self, row: int, col: int, direction: Tuple[int, int]) -> Optional[Tuple[int, int]]:
-        curr_row = row
-        curr_col = col
-
         steps = 0
         while self.max_neighbour_steps is None or steps < self.max_neighbour_steps:
-            curr_row += direction[0]
-            curr_col += direction[1]
-            if curr_row < 0 or curr_row >= self.num_rows:
+            row += direction[0]
+            col += direction[1]
+            if row < 0 or row >= self.num_rows:
                 break
-            if curr_col < 0 or curr_col >= self.num_cols:
+            if col < 0 or col >= self.num_cols:
                 break
 
-            if self.get(curr_row, curr_col) != Tile.FLOOR:
-                return (curr_row, curr_col)
+            if self.get(row, col) != Tile.FLOOR:
+                return (row, col)
             steps += 1
 
         return None
@@ -89,7 +86,7 @@ class Layout:
             yield self.get(nrow, ncol)
 
     def count_neighbours(self, row: int, col: int) -> int:
-        return len([tile for tile in self.neighbours(row, col) if tile == Tile.OCCUPIED])
+        return sum(1 for tile in self.neighbours(row, col) if tile == Tile.OCCUPIED)
 
 
 def run(layout: Layout) -> int:

day13/day13.hs

@@ -0,0 +1,47 @@
+module Day13 where
+
+import AoC
+
+import Data.List
+import Data.List.Split
+import Data.Maybe
+import Data.Ord
+import Data.Tuple
+
+-- | inverse integer modulus, "remainder until the next multiple of d"
+--
+-- @(n + n `'invMod'` d) `'mod'` d == 0@
+invMod :: Integral a => a -> a -> a
+invMod n d | r == 0 = 0
+           | otherwise = d - r
+           where r = n `mod` d
+
+-- | @'combineRemainders' (r1, d1) (r2, d2) = (r3, d3)@ combines a relation of the form
+--
+-- @
+-- x = r1 (mod d1)
+-- x = r2 (mod d2)
+-- @
+--
+-- into a single relation
+--
+-- @
+-- x = r3 (mod d3)
+-- @
+--
+-- @d1@ should be larger than @d2@ for better performance.
+combineRemainders :: (Integral a) => (a, a) -> (a, a) -> (a, a)
+combineRemainders (r1, d1) (r2, d2) = (fromJust . find (\x -> x `mod` d2 == r2) $ [r1,d1+r1..], d1*d2)
+
+part1 :: Int -> [Int] -> Int
+part1 arr = uncurry (*) . minimumBy (comparing snd) . map (toSnd $ invMod arr)
+    where toSnd f x = (x, f x)
+
+part2 :: [Maybe Int] -> Int
+part2 = fst . foldl1 combineRemainders . map (\(r, d) -> (r `invMod` d, d)) . catMaybes . map sequence . enumerate 0
+    where enumerate start (x:xs) = (start, x) : enumerate (succ start) xs
+          enumerate _ [] = []
+
+main = runAoC (intoTuple . map (map (fmap read . justIf (/="x")) . splitOn ",") . lines) (uncurry part1 . fmap catMaybes) (part2 . snd)
+    where intoTuple [[Just x], y] = (x, y)
+          justIf p x = if p x then Just x else Nothing

test.sh

@@ -34,7 +34,7 @@ for day in day*; do
 		echo -n "$solution... "
 
 		case "${solution##*/}" in
-			example.txt|.*)
+			example*|.*)
 				echo SKIP
 				continue
 		esac