1 files changed, 59 insertions, 0 deletions
diff --git a/day04/main.hs b/day04/main.hs
new file mode 100644
index 0000000..1904c88
--- /dev/null
+++ b/day04/main.hs
@@ -0,0 +1,59 @@
+module Main where
+
+import Data.Foldable (find)
+import Data.Maybe (fromJust, isJust)
+import Debug.Trace (trace, traceShow)
+import Utils
+
+type Board = [[Int]]
+
+toGroupsOfN :: Int -> [a] -> [[a]]
+toGroupsOfN n [] = []
+toGroupsOfN n lst = take n lst : toGroupsOfN n (drop n lst)
+
+rowBingo :: [Int] -> Board -> Bool
+rowBingo draws = any (all (`elem` draws))
+
+findBingo :: [Int] -> Board -> Maybe Int
+findBingo draws board =
+  let horizFound = rowBingo draws board
+      vertFound = rowBingo draws (transpose board)
+   in if horizFound || vertFound
+        then Just $ sumUnmarked draws board
+        else Nothing
+
+sumUnmarked :: [Int] -> Board -> Int
+sumUnmarked draws board =
+  let sumRowUnmarked row = filter (`notElem` draws) row $> sum
+   in board $> map sumRowUnmarked .> sum
+
+recur :: [Int] -> Int -> [Board] -> ()
+recur draws n boards
+  | n > length draws = ()
+  | otherwise =
+    let drawn = take n draws
+        notDrawn = drop n draws
+        bingoResults = boards $> mapWithIndex (findBingo drawn) .> filter (\(_, m) -> isJust m)
+        winningBoards = map (\(i, m) -> (i, last drawn * fromJust m)) bingoResults
+        nWinning = length winningBoards
+        indicesToRemove = map fst winningBoards
+        winningScores = map snd winningBoards
+        restBoards = removeAt indicesToRemove boards
+     in trace ("Found " ++ show nWinning ++ " results at " ++ show n ++ ": " ++ show winningScores ++ ", boards left: " ++ show (length restBoards)) $
+          recur draws (n + 1) restBoards
+
+run :: [Int] -> [Board] -> ()
+run draws = recur draws 1
+
+main :: IO ()
+main =
+  do
+    contents <- getContents
+    let input =
+          contents
+            $> lines
+            .> filter (not . null)
+
+    let draws = head input $> splitOn (== ',') .> map read :: [Int]
+    let boards = tail input $> map (words .> map read) .> toGroupsOfN 5 :: [Board]
+    run draws boards $> print