Solve day 17

Author: Demindiro

2021/17/main.hs

@@ -0,0 +1,23 @@
+step (vx, vy) (x, y) = ((vx - signum vx, vy - 1), (x + vx, y + vy))
+
+inArea ((lx, ly), (ux, uy)) (x, y) = f lx ux x && f ly uy y
+  where f a b v = a <= v && v <= b
+
+simulate t@((_, ly), (ux, _)) vel = (inArea t p, (v, p))
+  where cond (_, p@(x, y)) = inArea t p || x > ux || y < ly
+        (v, p) = until cond (uncurry step) (vel, (0, 0))
+
+testVels = [(x, y) | x <- [1..], y <- [x^2+1, x^2..(-(x^2)-1)]]
+
+solve a@(_, (ux, _)) = map (snd . fst)
+                       $ filter (fst . snd)
+                       $ takeWhile c
+                       $ map (\p -> (p, simulate a p)) testVels
+  where c (_, (_, (_, (x, _)))) = x <= ux * 2
+
+maxHeight y = (y + 1) * y `div` 2
+
+test  = ((20, -10), (30, -5))
+input = ((128, -142), (160, -88))
+
+main = mapM_ print $ sequence [maxHeight . maximum, length] $ solve input