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module Main (main) where
import Control.Monad (when)
import Data.List (foldl', sort)
import System.Exit (die)
exampleExpectedOutput = 35
exampleExpectedOutput2 = 220
parseInput :: String -> IO [Int]
parseInput filename = do
input <- readFile filename
return $ map read $ lines input
compute :: [Int] -> Int
compute jolts = result $ foldl' compute' (0, 0, 0) $ sort jolts
where
compute' (prev, ones, threes) jolt
| jolt - prev == 1 = (jolt, ones + 1, threes)
| jolt - prev == 3 = (jolt, ones, threes + 1)
result (_, ones, threes) = ones * (threes + 1)
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
example2 <- parseInput "example2"
let exampleOutput2 = compute example2
when (exampleOutput2 /= exampleExpectedOutput2) (die $ "example2 failed: got " ++ show exampleOutput2 ++ " instead of " ++ show exampleExpectedOutput2)
input <- parseInput "input"
print $ compute input
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