day6: Complete second puzzle

6/fishexploder.hs

@@ -6,28 +6,42 @@ main = do
   let
     fish = parseFish input
   (putStrLn . show . solution1) fish
+  (putStrLn . show . solution2) fish
 
 solution1 :: [Int] -> Int
-solution1 = length . (simulateDays 80)
+solution1 = sum . (simulateDays 79)
+
+solution2 :: [Int] -> Int
+solution2 = sum . (simulateDays 255)
 
 parseFish :: String -> [Int]
 parseFish = (map read) . (splitByString ",")
 
-simulateDays :: Int -> [Int] -> [Int]
-simulateDays days fish = foldr (\f acc -> f acc) fish (replicate days tickDay)
+initBuffer :: [Int] -> [Int]
+initBuffer initialFish = map occurrences [0..8]
+  where
+    occurrences x = length (filter (==x) initialFish)
 
-tickDay :: [Int] -> [Int]
-tickDay [] = []
-tickDay (fish:otherFish)
-  | fish == 0 = 6:8:(tickDay otherFish)
-  | otherwise = (fish - 1):(tickDay otherFish)
+simulateDays :: Int -> [Int] -> [Int]
+simulateDays days initialFish = foldl tickDay (initBuffer initialFish) [0..days]
+  where
+    tickDay :: [Int] -> Int -> [Int]
+    tickDay fish day = map fishMultiplier [0..length(fish)-1]
+      where
+        fishMultiplier :: Int -> Int
+        fishMultiplier i
+          | i == addedTo =
+            (fish !! i) + (fish !! dayFish)
+          | otherwise =
+            fish !! i
+            where
+              dayFish = day `rem` 9
+              addedTo = (dayFish + 7) `rem` 9
 
 -- Tests
 
 testInput = "3,4,3,1,2"
 testParsed = parseFish testInput
 
-test1 = solution1 (parseFish testInput)
-
-testTick = (tickDay . tickDay) testParsed
-testSimulate = length (simulateDays 80 testParsed)
+test1 = solution1 (parseFish testInput) -- 5934
+test2 = solution2 (parseFish testInput) -- 26984457539