2020-10 in haskell

2020/10-Adapter_Array/first.hs

@@ -0,0 +1,31 @@
+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