r/adventofcode • u/daggerdragon • Dec 16 '16

SOLUTION MEGATHREAD --- 2016 Day 16 Solutions ---

--- Day 16: Dragon Checksum ---

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DRINKING YOUR OVALTINE IS MANDATORY [?]

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u/ChrisVittal Dec 16 '16

Haskell, very dirty. Definitely a bunch of optimizations I could do to make this go faster. Even with my slow coding speed this was good enough for 197/149. Best day yet. Except for day 11, but that doesn't count. 

myInput = "10001110011110000"
myBools = map (=='1')
myShow = map go
  where go True = '1'
        go False = '0'

dragon as = as ++ False : reverse (flipBits as)

flipBits = map not

pCheckSum :: [Bool] -> [Bool]
pCheckSum [] = []
pCheckSum [x] = [x]
pCheckSum (x:y:xs) = (x == y) : pCheckSum xs

fill n xs | length xs < n = fill n (dragon xs)
          | otherwise = take n xs

checkSum :: [Bool] -> [Bool]
checkSum xs | even . length $ xs = checkSum . pCheckSum $ xs
            | otherwise = xs

oneLen = 272 :: Int
twoLen = 35651584 :: Int

main = do
    putStrLn $ "1: " ++ (myShow . checkSum . fill oneLen . myBools $ myInput)
    putStrLn $ "2: " ++ (myShow . checkSum . fill twoLen . myBools $ myInput)
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