Day 11

data/energy.txt

+4438624262
+6263251864
+2618812434
+2134264565
+1815131247
+2612457325
+8585767584
+7217134556
+2825456563
+8248473584
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src/AOC-11a.hs

 module Main where
 
+import Data.Array
+import qualified Data.Set as S
+
+type Position = (Int,Int)
+
+loadArray :: String -> Array Position Int
+loadArray s = array bds [ ((cx,rx),read [val])
+                        | (rx,row) <- zip [1..] rows
+                        , (cx,val) <- zip [1..] row
+                        ]
+  where
+  rows = lines s
+  nx = length (head rows)
+  ny = length rows
+  bds = ((1,1),(nx,ny))
+
+showArray :: Array Position Int -> String
+showArray arr = unlines [ [ head . show $ arr ! (x,y) 
+                          | x <- [xMin..xMax] 
+                          ]
+                        | y <- [yMin..yMax] 
+                        ] where
+  ((xMin,yMin),(xMax,yMax)) = bounds arr
+
+neighbors :: Array Position a -> Position -> [Position]
+neighbors arr (x,y) =
+  [ (x',y') 
+  | x' <- [x-1..x+1], y' <- [y-1..y+1]
+  , inRange (bounds arr) (x',y')
+  , (x',y') /= (x,y)
+  ]
+
+step :: (Array Position Int,Int) -> (Array Position Int,Int)
+step (as,nflashes) =  iter S.empty . incr $ as where
+  incr = ((+1) <$>)
+  iter :: S.Set Position -> Array Position Int -> (Array Position Int,Int)
+  iter hasFlashed arr
+    | S.null newFlash = (discharge arr,nflashes + S.size hasFlashed)
+    | otherwise = iter mightFlash $ accum (+) arr 
+        [ (n,1) | p <- S.toList newFlash, n <- neighbors arr p ]
+    where
+    mightFlash = S.fromList [ p | p <- range (bounds arr), arr ! p > 9]
+    newFlash = mightFlash S.\\ hasFlashed
+
+discharge :: Array Position Int -> Array Position Int
+discharge = (reset <$>) where
+  reset v
+    | v > 9 = 0
+    | otherwise = v
+
+allDischarged :: Array Position Int -> Bool
+allDischarged = all (==0) . elems
+
 main :: IO ()
-main = pure ()
+main = do
+  arr <- loadArray <$> readFile "data/energy.txt"
+  let sync = length . takeWhile (not . allDischarged . fst). iterate step $ (arr,0)
+  print sync
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test/energy.txt

+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
\ No newline at end of file