1 files changed, 21 insertions(+), 31 deletions(-)

M 2022/15.hs

@@ 5,7 5,7 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 module Main where
 
-import Qulude hiding ( rotate )
+import Qulude
 
 --import Data.Array ( (!) )
 import qualified Data.Array as Array


@@ 40,40 40,30 @@ parser = many sensor
 dist :: Point -> Point -> Int
 dist (x0,y0) (x1,y1) = abs (x1 - x0) + abs (y1 - y0)
 
-isCovered :: Point -> Sensor -> Bool
-isCovered p (s, b) = dist s p <= dist s b
+f y (s@(sx,sy), b) = if h > d then Nothing else Just $ (sx - l, sx + l + 1)
+  where d = dist s b
+        h = abs (sy - y)
+        l = d - h
 
-bounds :: [ Sensor ] -> Maybe (Point, Point)
-bounds [] = Nothing
-bounds ((s@(x,y),b):ss) =
-  let t = dist s b in
-  let ((x0,y0), (x1,y1)) = ((x-t,y-t),(x+t,y+t)) in
-  case bounds ss of
-    Nothing -> Just ((x0,y0), (x1,y1))
-    Just ((x0',y0'), (x1',y1')) ->
-      Just ((min x0 x0', min y0 y0'), (max x1 x1', max y1 y1'))
+k y = List.sortOn fst . catMaybes . fmap (f y)
 
-partA y ss = let Just ((x0,_),(x1,_)) = bounds ss in count [ check (x, y) | x <- [x0..x1] ]
- where check p = or $ fmap (\s@(_,b) -> p /= b && isCovered p s) ss
+partA y ss = let i:is = k y ss in g (-nbs) i is
+  where g n (x,y) [] = n + (y-x)
+        g n (x,y) ((x',y'):is) | x' <= y = g n (x,max y y') is
+        g n (x,y) ((x',y'):is) | y < x' = g (n+y-x) (x',y') is
+        bs = distinct $ fmap snd ss
+        nbs = count $ fmap ((==) y . snd) bs
 
---partB m ss = head [ tf x y | x <- [0..m], y <- [0..m], check (x,y) ]
- --where check p = not $ or $ fmap (\s -> (isCovered p s)) ss
-       --tf x y = x * 4000000 + y
-
-rotate a (x, y) = (x*cos a - y*sin a, x*sin a + y*cos a)
-
-partB _ ss = [ (f a b, a, b) | (a, _) <- ss, (b, _) <- ss ]
-  where pi4 = pi / 4
-        sq2 = sqrt 2 / 2
-        t (x, y) = (fromIntegral x, fromIntegral y)
-        f a b =
-          let (rax, ray) = rotate pi4 (t a) in
-          let (rbx, rby) = rotate pi4 (t b) in
-          (round $ (rax - rbx)/sq2, round $ (ray - rby)/sq2)
+partB m ss = g 0
+  where g y = h y (k y ss)
+        h y ((_,b):is) | b <= 0 = h y is
+        h y ((_,b):_) | b > m = g (succ y)
+        h y ((a,b):(a',b'):is) | b < a' = b * 4000000 + y
+        h y ((a,b):(a',b'):is) | otherwise = h y $ (a, max b b'):is
 
 main :: IO ()
 main = with parser $ do
   run' "15.example" "a example" (partA 10) 26
-  --run' "15.input" "a input" (partA 2000000) 5299855
-  run "15.example" "b example" (partB 20)
-  --run "15.input" "b input" (partB 4000000)
+  run' "15.input" "a input" (partA 2000000) 5299855
+  run' "15.example" "b example" (partB 20) 56000011
+  run' "15.input" "b input" (partB 4000000) 13615843289729