@@ -2002,18 +2002,24 @@ day20a = V.minIndex . V.fromList -- hijacking minIndex from Vector
20022002 . iterate (map step)
20032003```
20042004
2005- However, we could also be sneaky and just find the "maximum" normed initial
2006- vector, which is correct in the case where all of our initial accelerations are
2007- differently normed, and sometimes correct in the case where we have duplicated
2008- accelerations.
2005+ However, we are really just looking for the asymptotic behavior. In the long
2006+ run, the distance is dominated by the ` |a| t^2 ` term, so we really just need
2007+ to look for the particle with the highest normed initial acceleration.
20092008
20102009``` haskell
20112010day20a :: System -> Int
20122011day20a = V. minIndex . V. fromList
2013- . (map . fmap ) norm
2012+ . (map . fmap ) norm-- [Particle Point] -> [Particle Int]
20142013 . parse
20152014```
20162015
2016+ The ` Ord ` instance of ` Particle Int ` is such that it sorts first by the ` _pAcc `
2017+ field, then the ` _pVel ` field, then the ` _pPos ` field. So it'll find first the
2018+ highest normed acceleration, and break ties using the highest normed velocity.
2019+ However, this tie breaking isn't actually sound -- there are situations where
2020+ this won't be true. However, there were no ties in my data set so this method
2021+ was ok :)
2022+ 20172023For part 2, we can define a function that takes out all "duplicated" points,
20182024using a frequency map and filtering for frequencies greater than 1:
20192025
@@ -2058,14 +2064,14 @@ parse :: String -> System
20582064parse = map parseLine . lines
20592065 where
20602066 parseLine :: String -> Particle Point
2061- parseLine (map (read . filter numChar ). splitOn" ," -> [pX,pY,pZ,vX,vY,vZ,aX,aY,aZ])
2067+ parseLine (map (read . filter num ). splitOn" ," -> [pX,pY,pZ,vX,vY,vZ,aX,aY,aZ])
20622068 = P { _pAcc = L. V3
20632069 , _pVel = L. V3
20642070 , _pPos = L. V3
20652071 }
20662072 parseLine _ = error " No parse"
2067- numChar :: Char -> Bool
2068- numChar c = isDigit c || c == ' -'
2073+ num :: Char -> Bool
2074+ num c = isDigit c || c == ' -'
20692075```
20702076
20712077### Day 20 Benchmarks
0 commit comments