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Day 7, Part 2

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daniele 2024-12-07 15:33:03 +01:00
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import Data.List (transpose)
import Data.List.Split (splitOn)
type Equation = (Int, [Int])
concatInt :: Int -> Int -> Int
concatInt x y = read $ show x ++ show y
isSolvable :: Int -> Equation -> Bool
isSolvable cur (result, []) = cur == result
isSolvable cur (result, [x]) = cur + x == result || cur * x == result || cur `concatInt` x == result
isSolvable cur (result, x:y:ys) = isSolvable (cur + x + y) (result, ys)
|| isSolvable ((cur + x) * y) (result, ys)
|| isSolvable ((cur + x) `concatInt` y) (result, ys)
|| isSolvable (cur * x + y) (result, ys)
|| isSolvable (cur * x * y) (result, ys)
|| isSolvable ((cur * x) `concatInt` y) (result, ys)
|| isSolvable ((cur `concatInt` x) + y) (result, ys)
|| isSolvable ((cur `concatInt` x) * y) (result, ys)
|| isSolvable ((cur `concatInt` x) `concatInt` y) (result, ys)
main = do
[x, y] <- transpose . map (splitOn ":") . lines <$> readFile "day7.txt"
let results = map read x
values = map read <$> map words y
equations = zip results values
print . sum . map fst $ filter (isSolvable 0) equations