2024-10

inputs/2024/10.txt

@@ -0,0 +1,57 @@
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solutions/solutions.cabal

@@ -1157,3 +1157,8 @@ executable sln_2024_09
   import:              day
   main-is:             2024/09.hs
   build-depends:       array, containers
+
+executable sln_2024_10
+  import:              day
+  main-is:             2024/10.hs
+  build-depends:       array

solutions/src/2024/10.hs

@@ -0,0 +1,49 @@
+{-|
+Module      : Main
+Description : Day 10 solution
+Copyright   : (c) Eric Mertens, 2024
+License     : ISC
+Maintainer  : [email protected]
+
+<https://adventofcode.com/2024/day/10>
+
+>>> :{
+:main + "89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732
+"
+:}
+36
+81
+
+-}
+module Main where
+
+import Advent (arrIx, getInputArray)
+import Advent.Coord (Coord, cardinal)
+import Advent.Search (dfs)
+import Data.Array.Unboxed (UArray, (!), assocs)
+
+-- | >>> :main
+-- 778
+-- 1925
+main :: IO ()
+main =
+ do input <- getInputArray 2024 10
+    print (part1 input)
+    print (part2 input)
+
+part1 :: UArray Coord Char -> Int
+part1 a = length [() | (start, '0') <- assocs a, i <- dfs step start, a ! i == '9']
+  where
+    step x = [y | y <- cardinal x, Just (succ (a ! x)) == arrIx a y ]
+
+part2 :: UArray Coord Char -> Int
+part2 a = length [() | (start, '0') <- assocs a, (i, _) <- dfs step (start, []), a ! i == '9']
+  where
+    step (x, xs) = [(y, x : xs) | y <- cardinal x, Just (succ (a ! x)) == arrIx a y]