From 9e104a7ffbd3b6e57b98b9103a4b532802e47d52 Mon Sep 17 00:00:00 2001
From: Neil Smith <neil.git@njae.me.uk>
Date: Thu, 9 Dec 2021 16:18:30 +0000
Subject: [PATCH] Tidying, added blog link

---
 advent-of-code21.cabal |  2 +-
 advent09/Main.hs       | 32 ++++++++++----------------------
 2 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/advent-of-code21.cabal b/advent-of-code21.cabal
index 9e50851..d7c0fa8 100644
--- a/advent-of-code21.cabal
+++ b/advent-of-code21.cabal
@@ -128,4 +128,4 @@ executable advent08a
 executable advent09
   import: common-extensions, build-directives
   main-is: advent09/Main.hs
-  build-depends: array, containers
+  build-depends: array, containers, linear
diff --git a/advent09/Main.hs b/advent09/Main.hs
index 4cd269e..a5c4ccc 100644
--- a/advent09/Main.hs
+++ b/advent09/Main.hs
@@ -1,30 +1,26 @@
--- Writeup at https://work.njae.me.uk/2021/12/09/advent-of-code-2021-day-8/
-
+-- Writeup at https://work.njae.me.uk/2021/12/09/advent-of-code-2021-day-9/
 
 import Data.Array 
 import Data.Char
--- import Data.Maybe
-import Data.List hiding ((\\))
+import Data.List (sort)
 import qualified Data.Set as S
 import Data.Set ((\\))
+import Linear (V2(..), (^+^))
 
-
-type Coord = (Int, Int) -- (row, column)
+type Coord = V2 Int
 type Grid = Array Coord Int
 type Basin = S.Set Coord
 
 main :: IO ()
 main = 
-  do  text <- readFile "data/advent09.txt"
+  do  text <- readFile "data/advent09a.txt"
       let grid = mkGrid text
       print $ bounds grid
       print $ part1 grid
-      -- print $ lowPoints grid
-      -- print $ breadthFirstSearch grid (S.singleton (4, 6)) S.empty
       print $ part2 grid
 
 mkGrid :: String -> Grid
-mkGrid text = listArray ((0, 0), (r, c)) $ map digitToInt $ concat rows
+mkGrid text = listArray ((V2 0 0), (V2 r c)) $ map digitToInt $ concat rows
   where rows = lines text
         r = length rows - 1
         c = (length $ head rows) - 1
@@ -70,16 +66,8 @@ breadthFirstSearch grid agenda basin
 
 
 neighbours :: Grid -> Coord -> [Coord]
-neighbours grid (r, c) = filter (gValid grid)  
-  [ (r + dr, c + dc) 
-  | (dr, dc) <- [(-1, 0), (1, 0), (0, -1), (0, 1)]
+neighbours grid here = filter (inRange (bounds grid))  
+  [ here ^+^ delta 
+  | delta <- [V2 -1 0, V2 1 0, V2 0 -1, V2 0 1]
   ]
-
-gValid :: Grid -> Coord -> Bool
-gValid grid (r, c)
-  | r < minR = False
-  | c < minC = False
-  | r > maxR = False
-  | c > maxC = False
-  | otherwise = True
-  where ((minR, minC), (maxR, maxC)) = bounds grid
+ 
-- 
2.34.1