Add day12 part 1

y2019/src/Day12.hs

@@ -1,5 +1,61 @@
 module Day12 (day12) where
 
+import Data.List
+import Data.List.Split
+
+data V = V { _x :: Int, _y :: Int, _z :: Int } deriving (Eq, Show)
+
+nullV :: V
+nullV = V 0 0 0
+
+data Moon = Moon { _pos :: V, _vel :: V } deriving (Eq, Show)
+
+parseLine :: String -> Moon
+parseLine input = Moon (V (getNb 0) (getNb 1) (getNb 2)) nullV
+  where input' = filter (\c -> not $ elem c "<>,") input
+        parts = splitOn " " input'
+        getNb x = read $ (!! 1) $ splitOn "=" $ (parts !! x)
+
+computeVelocity :: V -> [Moon] -> V
+computeVelocity pos@(V x y z) ((Moon (V ox oy oz) _):others) = V (curX + nextX) (curY + nextY) (curZ + nextZ)
+  where (V nextX nextY nextZ) = computeVelocity pos others
+        curX = veloChange x ox
+        curY = veloChange y oy
+        curZ = veloChange z oz
+        veloChange a b = if a > b
+                         then -1
+                         else if a < b
+                              then 1
+                              else 0
+computeVelocity _ [] = nullV
+
+applyVelocity :: [Moon] -> Moon -> Moon
+applyVelocity others cur@(Moon curPos@(V px py pz) (V vx vy vz)) = Moon newPos newVel
+  where (V nvx nvy nvz) = computeVelocity curPos others'
+        others' = filter (/= cur) others
+        newVel = V (vx + nvx) (vy + nvy) (vz + nvz)
+        newPos = V (px + vx + nvx)  (py + vy + nvy)  (pz + vz + nvz)
+
+computeStep :: [Moon] -> [Moon]
+computeStep moons = map (applyVelocity moons) moons
+
+moonEnergy :: Moon -> Int
+moonEnergy (Moon (V px py pz) (V vx vy vz)) = potentialEnergy * kineticEnergy
+  where potentialEnergy = (abs px) + (abs py) + (abs pz)
+        kineticEnergy = (abs vx) + (abs vy) + (abs vz)
+
 day12 :: IO ()
 day12 = do
   putStrLn "AoC 2019 day 12"
+
+  input <- getContents
+
+  let planets = map parseLine $ filter (not . null) $ splitOn "\n" input
+  let iteration = iterate computeStep planets
+
+  let at1000 = iteration !! 1000
+  putStrLn $ "Part 1: " ++ (show $ sum $ map moonEnergy $ at1000)
+
+  -- ok, inefficient, need something better
+  let idx = elemIndex planets $ tail iteration
+  putStrLn $ "Part 2: " ++ (show $ fmap (+1) idx)