Day 9 (incomplete, a done, b incorrect)

advent-of-code.cabal

@@ -88,14 +88,17 @@ executable aoc-08b
 executable aoc-09a
 executable aoc-09a
   import              : aoc-common
   import              : aoc-common
   main-is             : AOC-09a.hs
   main-is             : AOC-09a.hs
+  build-depends       : array
 
 
 executable aoc-09b
 executable aoc-09b
   import              : aoc-common
   import              : aoc-common
   main-is             : AOC-09b.hs
   main-is             : AOC-09b.hs
+  build-depends       : array
 
 
 executable aoc-10a
 executable aoc-10a
   import              : aoc-common
   import              : aoc-common
   main-is             : AOC-10a.hs
   main-is             : AOC-10a.hs
+  build-depends       : array
 
 
 executable aoc-10b
 executable aoc-10b
   import              : aoc-common
   import              : aoc-common

src/AOC-09a.hs

 module Main where
 module Main where
 
 
+import Data.Array
+
+makeHeightMap :: String -> Array (Int,Int) Int
+makeHeightMap s = array ((1,1),(mx,my)) entries where
+  rows = lines s
+  entries = [((x,y),z) | (x,row) <- zip [1..] (lines s)
+                       , (y,c) <- zip [1..] row
+                       , let z = read [c]
+                       ]
+  mx = length (rows)
+  my = length (head rows)
+
+heightAt :: Array (Int,Int) Int -> (Int,Int) -> Int
+heightAt arr pos =
+  if inRange (bounds arr) pos
+  then arr ! pos
+  else 10
+
+neighbors :: (Int,Int) -> [(Int,Int)]
+neighbors (x,y) = [(x-1,y),(x+1,y),(x,y-1),(x,y+1)]
+
+isLowPoint :: Array (Int,Int) Int -> (Int,Int) -> Bool
+isLowPoint arr pos = (arr ! pos) < minimum (map (heightAt arr) (neighbors pos))
+
+score :: Array (Int,Int) Int -> Int
+score heightMap = sum . map (+1) . map (heightMap !) . filter (isLowPoint heightMap) . range . bounds $ heightMap
+
 main :: IO ()
 main :: IO ()
-main = pure ()
+main = do
+  heightMap <- makeHeightMap <$> readFile "data/heightMap.txt"
+  print $ score heightMap
+

src/AOC-09b.hs

 module Main where
 module Main where
 
 
+import Data.Array
+import Data.List
+
+makeHeightMap :: String -> Array (Int,Int) Int
+makeHeightMap s = array ((1,1),(mx,my)) entries where
+  rows = lines s
+  entries = [((x,y),z) | (x,row) <- zip [1..] (lines s)
+                       , (y,c) <- zip [1..] row
+                       , let z = read [c]
+                       ]
+  mx = length (rows)
+  my = length (head rows)
+
+heightAt :: Array (Int,Int) Int -> (Int,Int) -> Int
+heightAt arr pos =
+  if valid arr pos
+  then arr ! pos
+  else 10
+
+valid :: (Ix k) => Array k v -> k -> Bool
+valid arr key = (`inRange` key) . bounds $ arr
+
+neighbors :: Array (Int,Int) Int -> (Int,Int) -> [(Int,Int)]
+neighbors arr (x,y) = filter (valid arr) [(x-1,y),(x+1,y),(x,y-1),(x,y+1)]
+
+isLowPoint :: Array (Int,Int) Int -> (Int,Int) -> Bool
+isLowPoint arr pos = (arr ! pos) < minimum (map (heightAt arr) (neighbors arr pos))
+
+lowPoints :: Array (Int,Int) Int -> [(Int,Int)]
+lowPoints arr = filter (isLowPoint arr) . range . bounds $ arr
+
+-- This code is wrong for the interpretation of a basin given by
+-- the problem.
+
+basin :: Array (Int,Int) Int -> (Int,Int) -> [(Int,Int)]
+basin arr pos = pos : iter pos (neighbors arr pos) where
+  iter :: (Int,Int) -> [(Int,Int)] -> [(Int,Int)]
+  iter _ [] = []
+  iter p (n:ns) 
+    | n `flowsTo` p = n : iter p ns ++ iter n (neighbors arr n)
+    | otherwise = iter p ns
+  flowsTo n p =
+    let target = heightAt arr n
+        flowPoints = filter ((< target) . (arr !)) . neighbors arr $ n
+    in flowPoints == [p]
+
 main :: IO ()
 main :: IO ()
-main = pure ()
+main = do
+  heightMap <- makeHeightMap <$> readFile "test/heightMap.txt"
+  putStr . unlines . map (show . sort) $ basin heightMap <$> lowPoints heightMap

test/heightMap.txt

+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
\ No newline at end of file