7

1 files changed, 22 insertions, 0 deletions

diff --git a/2024/7.hs b/2024/7.hs
new file mode 100644
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--- /dev/null
+++ b/2024/7.hs
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+{-# OPTIONS -Wno-incomplete-uni-patterns #-}
+import Control.Monad (guard)
+
+main :: IO ()
+main = do
+  let parse line = let (lhs, _ : rhs) = break (== ':') line
+                   in (read @Int lhs, map (read @Int) (words rhs))
+  input <- map parse . lines <$> getContents
+
+  let numdigs = go 1
+        where go !d n | n < 10 = d :: Int
+                      | otherwise = go (d+1) (n `quot` 10)
+  let a .|| b = a * 10 ^ numdigs b + b
+  
+  let evals _  _   acc [] = [acc]
+      evals p2 lhs acc (n:nums) = do
+        acc' <- [acc + n, acc * n] ++ (if p2 then [acc .|| n] else [])
+        guard (acc' <= lhs)
+        evals p2 lhs acc' nums
+
+  print $ sum [lhs | (lhs, nums) <- input, lhs `elem` evals False lhs 0 nums]
+  print $ sum [lhs | (lhs, nums) <- input, lhs `elem` evals True lhs 0 nums]