Solve day 11

Not using recursion may have cost me a bit of my remaining sanity.

Author: Demindiro

2021/11/input.txt

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+3265255276
+1537412665
+7335746422
+6426325658
+3854434364
+8717377486
+4522286326
+6337772845
+8824387665
+6351586484

2021/11/main.hs

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+parseInput = foldl (++) []
+           . map (\(y, l) -> map (\(x, c) -> ((x, y), read [c])) l)
+           . zip [0..]
+           . map (zip [0..])
+           . lines
+
+powerup = map (\(p, i) -> (p, i + 1))
+
+flash l = l >>= (\(p, i) -> if i >= 10 then [p] else [])
+
+flashN l = l >>= neighbours
+
+neighbours (x, y) = [ (x + x', y + y')
+                    | x' <- [-1..1]
+                    , y' <- [-1..1]
+                    , (x', y') /= (0, 0)
+                    ]
+
+count p = length . filter (==p)
+
+ripple n = map (\(p, i) -> (p, if i /= 0 then i + count p n else i))
+
+drain = map (\(p, i) -> (p, if i >= 10 then 0 else i))
+
+step l = snd $ until ((==[]) . fst) m (f', r')
+  where
+    l'       = powerup l
+    f'       = flashN $ flash l'
+    r'       = ripple f' (drain l')
+    m (_, r) = let f = flash r
+               in  (f, ripple (flashN f) (drain r))
+
+part1 x = fst $ foldl f (0, x) [1..100]
+  where
+    f (s, p) _ = let p' = step p
+                 in  (s + count 0 (map snd p'), p')
+
+part2 x = fst $ until (all (== 0) . map snd . snd)
+                      (\(x, y) -> (x + 1, step y))
+                      (0, x)
+
+main = fmap parseInput (readFile "input.txt")
+   >>= mapM_ print . sequence [part1, part2]

2021/11/test.txt

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+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526