Part 1

day8/main.hs

@@ -1,8 +1,10 @@
 #! /usr/bin/env -S"ANSWER=42" nix-shell
 #! nix-shell -p ghcid
 #! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [pretty-simple vector containers])"
-#! nix-shell -i "ghcid -c 'ghci -Wall' -T main"
+#! nix-shell -i "ghcid -c 'ghci' -T main"
 
+{-# OPTIONS_GHC -Wall -Wincomplete-uni-patterns #-}
+{-# OPTIONS_GHC -Wno-unused-top-binds #-}
 {-# LANGUAGE OverloadedStrings #-}
 
 import Text.Pretty.Simple
@@ -11,7 +13,9 @@ import Text.Pretty.Simple
 import Data.Vector (Vector)
 import Debug.Trace (trace)
 import Data.List (unfoldr)
+import Data.IntMap.Strict (IntMap)
 import qualified Data.Vector as V
+import qualified Data.IntMap.Strict as M
 
 data Op = OpNop
         | OpJmp !Int
@@ -66,16 +70,29 @@ vmFromInput input = initialVM (ins input)
 
 -- Find smallest looping prefix in list of Int, returns associated pgmAccumulator
 solvePart1 :: VirtualMachine -> Int
-solvePart1 vm = undefined vm
+solvePart1 vm0 =
+  snd . last $ shortestCycleOn $ (\vm -> (pgmCounter vm, pgmAccumulator vm)) <$> unfoldr stepVM vm0
 
 -- Shortest cycle in [Int]
-shortestCycle :: [Int]
+shortestCycle :: [Int] -> [Int]
+shortestCycle ix = reverse $ go M.empty ix []
+  where
+    go :: (IntMap ()) -> [Int] -> [Int] -> [Int]
+    go mem (x:_ ) ys | (mem M.!? x) /= Nothing = ys
+    go mem (x:xs) ys | otherwise               = go (M.insert x () mem) xs (x:ys)
+    go _ [] ys                                 = ys
+
+shortestCycleOn :: [(Int,Int)] -> [(Int,Int)]
+shortestCycleOn tx = zip (shortestCycle cx) ax
+  where
+    (cx, ax) = unzip tx
 
 main :: IO ()
 main = do
   putStrLn "Day 8 - Part 1"
   putStrLn ":: Tests"
   pPrint exampleData
-  print $ take 10 $ (\vm -> (pgmCounter vm, pgmAccumulator vm)) <$> unfoldr stepVM (vmFromInput exampleData)
   putStrLn ":: Solving part 1"
-  print $ solvePart1 (vmFromInput exampleData)
+  pPrint $ solvePart1 (vmFromInput exampleData)
+  input <- lines <$> readFile "day8/input"
+  pPrint $ solvePart1 (vmFromInput input)

template.hs

@@ -1,8 +1,10 @@
 #! /usr/bin/env -S"ANSWER=42" nix-shell
 #! nix-shell -p ghcid
-#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [shower])"
+#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [])"
-#! nix-shell -i "ghcid -c 'ghci -Wall' -T main"
+#! nix-shell -i "ghcid -c 'ghci' -T main"
 
+{-# OPTIONS_GHC -Wall -Wincomplete-uni-patterns #-}
+{-# OPTIONS_GHC -Wno-unused-top-binds #-}
 {-# LANGUAGE OverloadedStrings #-}
 
 main :: IO ()