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day 12 part 2: invert the search

This commit is contained in:
Quinten Kock 2022-12-12 06:44:18 +01:00
parent afa4f955ef
commit 6d5f5c7910
1 changed files with 9 additions and 7 deletions
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16
2022/day12.hs
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@ -17,7 +17,7 @@ bfs heightmap ((q@(x,y), dist):queue) visited = if usable
where
current = heightmap A.! q
inRange (x,y) = let (bx, by) = snd (A.bounds heightmap) in x >= 0 && x <= bx && y >= 0 && y <= by
reachable coord = inRange coord && (heightmap A.! coord) <= current + 1
reachable coord = inRange coord && (heightmap A.! coord) >= current - 1
neighs = filter reachable [(x+1, y), (x-1, y), (x, y+1), (x, y-1)]
usable = case M.lookup q visited of
Nothing -> True
@ -36,7 +36,7 @@ findIndex2 f xss = listToMaybe xs2 where
xs2 = mapMaybe (uncurry augment) xs
augment a (Just b) = Just (a,b)
augment a Nothing = Nothing
main = do
m <- lines <$> getContents
@ -44,11 +44,13 @@ main = do
let target = fromJust $ findIndex2 (=='E') m
let heightmap = A.listArray ((0,0), (length m - 1, length (head m) - 1)) (concatMap (map toHeight) m)
print heightmap
let final = bfs heightmap [(start, 0)] M.empty
let final = bfs heightmap [(target, 0)] M.empty
print $ final M.! target
putStr "part 1: "
print $ final M.! start
pure ()
putStr "part 2: "
let starts = map fst $ filter (\x -> snd x == toHeight 'a') (A.assocs heightmap)
let dists = mapMaybe (`M.lookup` final) starts
print $ minimum dists