Add 2020 day 14 p2

haskellAoC/inputs/2020/14_test

@@ -1,4 +0,0 @@
-mask = XXXXXXXXXXXXXXXXXXXXXXXXXXXXX1XXXX0X
-mem[8] = 11
-mem[7] = 101
-mem[8] = 0

haskellAoC/src/Y2020/Day14.hs

@@ -3,48 +3,105 @@ module Y2020.Day14 (y20day14) where
 import Data.Bits
 import qualified Data.Map as M
 
-type Bitmask = M.Map Int Bool
+-- map offset -> 1 (just true), 0 (just false), X (nothing)
+-- list of combinations values for the Xs
+type Bitmask = (M.Map Int (Maybe Bool), [Int])
 
-data Instruction = UpdateBitMask [(Int, Bool)] | SetMemory Int Int deriving (Show)
+data Instruction = UpdateBitMask [(Int, Maybe Bool)] | SetMemory Int Int deriving (Show)
 
 data State = State {
   bitmask :: Bitmask
-  , memory :: M.Map Int Int -- [(Int, Int)]
+  , memory :: M.Map Int Int
   } deriving (Show)
 
+parseBitMask :: Int -> String -> [(Int, Maybe Bool)]
+parseBitMask _ [] = []
+parseBitMask offset (x:xs) =
+  let next = (parseBitMask (offset + 1) xs) in
+    case x of
+      '1' -> (offset, Just True):next
+      '0' -> (offset, Just False):next
+      _ -> (offset, Nothing):next
+
 parseInput :: [String] -> Instruction
 parseInput ["mask", "=", mask] = UpdateBitMask $ parseBitMask 0 $ reverse mask
   where
-    parseBitMask :: Int -> String -> [(Int, Bool)]
-    parseBitMask _ [] = []
-    parseBitMask offset (x:xs) =
-      let next = (parseBitMask (offset + 1) xs) in
-        case x of
-          '1' -> (offset, True):next
-          '0' -> (offset, False):next
-          _ -> next
 parseInput ["mem", offset, "=", value] = SetMemory (read offset) (read value)
 parseInput s = error $ "Invalid line: " ++ (unwords s)
 
 applyInstructionP1 :: State -> Instruction -> State
 applyInstructionP1 (State _ mem) (UpdateBitMask updates) = State newMask mem
-  where newMask = M.fromList updates
+  where newMask = (M.fromList updates, [])
-applyInstructionP1 (State bm mem) (SetMemory offset value) = State bm newMemory
+applyInstructionP1 (State (bm, _) mem) (SetMemory offset value) = State (bm, []) newMemory
   where newMemory = M.insert offset (maskValue value) mem
         maskValue val = checkBit val $ finiteBitSize val
           where checkBit v (-1) = v
                 checkBit v offset' = checkBit newVal (offset' - 1)
                   where newVal = case offset `M.lookup` bm of
-                                   Just True  -> v `setBit` offset'
+                                   Just (Just True)  -> v `setBit` offset'
-                                   Just False -> v `clearBit` offset'
+                                   Just (Just False) -> v `clearBit` offset'
-                                   Nothing    -> v
+                                   _                 -> v
+
+-- arg1: available combinations
+-- arg2: variable offsets
+-- arg3: final combinations
+computeBitCombinations :: [Int] -> [Int] -> [Int]
+computeBitCombinations [] (b:bs) = computeBitCombinations [0, 0 `setBit` b] bs
+computeBitCombinations done [] = done
+computeBitCombinations done (b:bs) = computeBitCombinations (concatMap (\x -> [x, x `setBit` b]) done) bs
+
+-- p2 :
+-- compute value (of address) with mask considering Xs => &0, other offsets: |
+-- compute all possible values of Xs (X00X -> 0000, 0001, 1000, 1001)
+-- for each possible values of Xs, add initial masked value
+
+-- mask:            X1001X
+-- with address 42: 101010
+
+-- masked address : 011010 (26)
+-- 4 possibilities: 000000 (0)  + 26 = 26
+--                  000001 (1)  + 27 = 27
+--                  100000 (32) + 32 = 58
+--                  100001 (33) + 33 = 59
+
+-- mask:            00X0XX
+-- with address 26: 011010
+-- masked address:  010000 (16)
+
+-- 8 possibilities: 000000 (0)  + 16 = 16
+--                  000001 (1)  + 16 = 17
+--                  000010 (2)  + 16 = 18
+--                  000011 (3)  + 16 = 19
+--                  001000 (8)  + 16 = 24
+--                  001001 (9)  + 16 = 25
+--                  001010 (10) + 16 = 26
+--                  001011 (11) + 16 = 27
+
+applyInstructionP2 :: State -> Instruction -> State
+applyInstructionP2 (State _ mem) (UpdateBitMask updates) = State newMask mem
+  where newMask = (bitMask, variableCombinations)
+        variableCombinations = computeBitCombinations [] $ map fst $ filter ((== Nothing) . snd) $ updates
+        bitMask = M.fromList $ filter ((/= Just False) . snd) $ updates
+applyInstructionP2 (State (bm, var) mem) (SetMemory offset value) = newState
+  where newState  = State (bm, var) newMemory
+        newMemory = foldr (\k -> M.insert k value) mem addresses
+        addresses = map (\v -> v + offset') var
+        offset'   = checkBit offset $ finiteBitSize offset
+          where checkBit v (-1) = v
+                checkBit v o = checkBit newVal (o - 1)
+                  where newVal = case o `M.lookup` bm of
+                                   Just (Just True)  -> v `setBit` o
+                                   Just (Nothing)    -> v `clearBit` o
+                                   _                 -> v
+
 
 y20day14 :: [String] -> (String, String)
 y20day14 input = (part1, part2)
-  where part1 = show $ M.foldr (+) 0 $ memory endState
+  where part1 = show $ M.foldr (+) 0 $ memory endStateP1
-        part2 = show $ "WIP"
+        part2 = show $ M.foldr (+) 0 $ memory endStateP2
-        initialState = State M.empty M.empty
+        initialState = State (M.empty, []) M.empty
-        endState = foldl applyInstructionP1 initialState instructions
+        endStateP1 = foldl applyInstructionP1 initialState instructions
+        endStateP2 = foldl applyInstructionP2 initialState instructions
         instructions = map (parseInput . words . replaceBrackets) input
           where replaceBrackets ('[':xs) = ' ':(replaceBrackets xs)
                 replaceBrackets (']':xs) = ' ':(replaceBrackets xs)