From 06b14ed84c0a8ec11462f0a6f7397c3e3a52654d Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Tue, 8 Dec 2020 12:33:22 +0530
Subject: add initial day08 solution

---
 execs/Day08.hs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 execs/Day08.hs

(limited to 'execs')

diff --git a/execs/Day08.hs b/execs/Day08.hs
new file mode 100644
index 0000000..7d3fce8
--- /dev/null
+++ b/execs/Day08.hs
@@ -0,0 +1,45 @@
+module Main where
+
+import           Data.Set (Set)
+import qualified Data.Set as Set
+import           Data.Map (Map)
+import qualified Data.Map as Map
+import           Utils
+
+type Op = (String, Int)
+
+parseLine :: [String] -> Op
+parseLine [s, j] = (s, read (dropWhile (== '+') j))
+
+run :: Int -> Int -> Set Int -> Map Int Op -> Int
+run acc pc visited operations = if Set.member pc visited then acc else handleCase
+    where visited' = Set.insert pc visited
+          handleCase = 
+              case Map.lookup pc operations of
+                Just ("acc", v) -> run (acc + v) (pc + 1) visited' operations
+                Just ("nop", _) -> run acc (pc + 1) visited' operations
+                Just ("jmp", j) -> run acc (pc + j) visited' operations
+                _ -> acc
+
+doesEnd :: Int -> Int -> Set Int -> Map Int Op -> Bool
+doesEnd acc pc visited operations = not (Set.member pc visited) && handleCase
+    where visited' = Set.insert pc visited
+          handleCase = 
+              case Map.lookup pc operations of
+                Just ("acc", v) -> doesEnd (acc + v) (pc + 1) visited' operations
+                Just ("nop", _) -> doesEnd acc (pc + 1) visited' operations
+                Just ("jmp", j) -> doesEnd acc (pc + j) visited' operations
+                _ -> True -- pc has crossed the end!
+
+genAll :: [Op] -> [[Op]]
+genAll [] = []
+genAll (n@("nop",v):rest) = (("jmp",v):rest) : map (n:) (genAll rest)
+genAll (j@("jmp",v):rest) = (("nop",v):rest) : map (j:) (genAll rest)
+genAll (acc:rest) = map (acc:) $ genAll rest
+
+main :: IO ()
+main = do
+    n <- map (parseLine . words) . lines <$> readFile "input/08"
+    let solve1 = run 0 0 Set.empty . Map.fromList . zip [0..] 
+    print $ solve1 n
+    print $ solve1 $ head $ filter (doesEnd 0 0 Set.empty . Map.fromList . zip [0..]) $ genAll n
-- 
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