Day 24: Crossed Wires
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Haskell
Part 1 was trivial, just apply the operations and delay certain ones until you have all the inputs you need.
Code
import Control.Arrow
import Data.Bits
import Numeric
import qualified Data.Char as Char
import qualified Data.List as List
import qualified Data.Map as Map
parse s = (Map.fromList inputs, equations)
where
ls = lines s
inputs = map (take 3 &&& (== "1") . drop 5) . takeWhile (/= "") $ ls
equations = map words . filter (/= "") . tail . dropWhile (/= "") $ ls
operations = Map.fromList
[ ("AND", (&&))
, ("XOR", xor)
, ("OR", (||))
]
solveEquations is [] = is
solveEquations is (e:es)
| is Map.!? input1 == Nothing = solveEquations is (es ++ [e])
| is Map.!? input2 == Nothing = solveEquations is (es ++ [e])
| otherwise = solveEquations (Map.insert output (opfunc value1 value2) is) es
where
value1 = is Map.! input1
value2 = is Map.! input2
opfunc = operations Map.! operation
(input1:operation:input2:_:output:[]) = e
wireNumber prefix = List.filter ((prefix `List.isPrefixOf`) . fst)
>>> flip zip [0..]
>>> List.filter (snd . fst)
>>> List.map ((2 ^ ). snd)
>>> sum
part1 = uncurry solveEquations
>>> Map.toList
>>> wireNumber "z"
part2 (is, es) = List.intercalate "," . List.sort . words $ "z08 ffj dwp kfm z22 gjh jdr z31"
main = getContents
>>= print
. (part1 &&& part2)
. parse
For part 2 I tried symbolic solving to detect discrepancies but I wouldn’t achieve anything with it.
SymbolicEquation
data SymbolicEquation = Single { eqName :: String }
| Combine
{ eqName :: String
, eqOperation :: String
, eqLeft :: SymbolicEquation
, eqRight :: SymbolicEquation
}
deriving (Eq)
instance Show SymbolicEquation where
show (Single name) = name
show (Combine name op l r) = "(" ++ name ++ "= " ++ show l ++ " " ++ op ++ " " ++ show r ++ ")"
symbolicSolve is [] = is
symbolicSolve is (e:es)
| is Map.!? input1 == Nothing = symbolicSolve is (es ++ [e])
| is Map.!? input2 == Nothing = symbolicSolve is (es ++ [e])
| otherwise = symbolicSolve (Map.insert output (Combine output operation value1 value2) is) es
where
value1 = is Map.! input1
value2 = is Map.! input2
(input1:operation:input2:_:output:[]) = e
My solution was to use the dotEngine-function to translate the operations into a digraph in graphviz-style which I simply plotted and searched through using a python script.
dotEngine
dotEngine (input1:operation:input2:_:output:[]) = [
input1 ++ " -> " ++ output ++ " [ label=" ++ operation ++ "];"
, input2 ++ " -> " ++ output ++ " [ label=" ++ operation ++ "];"
]
I took a loook at the initial graph which was a vertical line with a few exception which I figured would be the misordered wires.
I did try some hardware-simulations in the far past to build bit-adders which helped me recognize patterns like carry calculation.
First I replaced all occurences of x__ XOR y__ -> w with x__ XOR y__ -> xor__ to recognize them more easily. The same with AND of xs and ys.
Using the following script I would then use some Regex to search for the rules that corresponded to carry calculations or structures I knew. The script would break exactly four times and I would then figure out what to switch by hand through looking at the updated graphViz.
Please excuse the bad coding style in the script, I had written it on the ipython-REPL.
python script
r = open("input").read()
for i in range(2, 45):
prevI = str(i - 1).zfill(2)
I = str(i).zfill(2)
forward = f"xor{I} AND carry{prevI} -> (\\w+)"
backward = f"carry{prevI} AND xor{I} -> (\\w+)"
m1 = re.search(forward, r)
m2 = re.search(backward, r)
if m1 is None and m2 is None:
print(forward, backward)
break
m = m1 or m2
r = r.replace(m.group(1), f"combinedCarry{I}")
forward = f"and{I} OR combinedCarry{I} -> (\\w+)"
backward = f"combinedCarry{I} OR and{I} -> (\\w+)"
m1 = re.search(forward, r)
m2 = re.search(backward, r)
if m1 is None and m2 is None:
print(forward, backward)
break
m = m1 or m2
r = r.replace(m.group(1), f"carry{I}")
open("input", "w").write()
When solving such a swapped wire problem I would then use my haskell function to plot it out again and stare at it for a few minutes until I understood wich parts belonged where.
The last one looked like this
In this one I needed to switch jdr and carry31 to make it work.
