From f36d3739a01216c2c0deb62d1a014812a016ca56 Mon Sep 17 00:00:00 2001
From: Javran Cheng <Javran.C@gmail.com>
Date: Sat, 6 Jan 2024 22:26:13 -0800
Subject: [PATCH] day 3 cleanup

---
 src/Javran/AdventOfCode/Y2023/Day3.hs | 74 +++++++++++++--------------
 1 file changed, 37 insertions(+), 37 deletions(-)

diff --git a/src/Javran/AdventOfCode/Y2023/Day3.hs b/src/Javran/AdventOfCode/Y2023/Day3.hs
index 288d8129..bfdb2e7d 100644
--- a/src/Javran/AdventOfCode/Y2023/Day3.hs
+++ b/src/Javran/AdventOfCode/Y2023/Day3.hs
@@ -1,33 +1,11 @@
-{-# LANGUAGE PatternGuards #-}
-{-# LANGUAGE ViewPatterns #-}
-{-# OPTIONS_GHC -Wno-deprecations #-}
-{-# OPTIONS_GHC -Wno-typed-holes #-}
-{-# OPTIONS_GHC -Wno-unused-imports #-}
-{-# OPTIONS_GHC -fdefer-typed-holes #-}
-
 module Javran.AdventOfCode.Y2023.Day3 () where
 
-{- HLINT ignore -}
-
-import Control.Applicative
 import Control.Monad
 import Data.Char
-import Data.Function
-import Data.Function.Memoize (memoFix)
-import qualified Data.IntMap.Strict as IM
-import qualified Data.IntSet as IS
-import Data.List
-import Data.List.Split hiding (sepBy)
 import qualified Data.Map.Strict as M
 import Data.Monoid hiding (First, Last)
-import Data.Semigroup
-import qualified Data.Set as S
-import qualified Data.Text as T
-import qualified Data.Vector as V
-import GHC.Generics (Generic)
 import Javran.AdventOfCode.GridSystem.RowThenCol.Uldr
 import Javran.AdventOfCode.Prelude
-import Text.ParserCombinators.ReadP hiding (count, get, many)
 
 data Day3 deriving (Generic)
 
@@ -58,6 +36,11 @@ parseSchematic inp = (M.fromList syms, nums)
       partitionEithers $
         fmap (\(coord, e) -> bimap (coord,) (coord,) e) tokens
 
+{-
+  Tests whether a number is adjacent to a coord (which is a symbol).
+
+  I feel it's easier that we draw this "rectangle" and see if symbol coordinate is inside.
+ -}
 isAdjacent :: (Coord, ANum) -> Coord -> Bool
 isAdjacent ((nr, nc), (_, nl)) (sr, sc) =
   nr - 1 <= sr && sr <= nr + 1 && nc - 1 <= sc && sc <= nc + nl
@@ -65,25 +48,42 @@ isAdjacent ((nr, nc), (_, nl)) (sr, sc) =
 instance Solution Day3 where
   solutionSolved _ = True
   solutionRun _ SolutionContext {getInputS, answerShow} = do
-    xs <- lines <$> getInputS
-    let (syms, nums) = parseSchematic xs
+    (syms, nums) <- parseSchematic . lines <$> getInputS
+    answerShow
+      . getSum
+      . foldMap
+        ( \n@(_, (v, _)) ->
+            {-
+              Note that we can further squeeze some performance by only feeding
+              the relevant 3 rows (with middle row being where the number is located)
+              of symbols instead of all of them and skip row range checks on
+              `isAdjacent`.
+              However given the scale of input data I don't think it worth the effort.
+             -}
+            if any (isAdjacent n) $ M.keys syms then Sum v else 0
+        )
+      $ nums
     do
-      let rs = filter (\n -> any (isAdjacent n) $ M.keys syms) nums
-      answerShow $ sum $ fmap (fst . snd) rs
-    let mayGearCoords :: [Coord]
+      let
+        -- Coordinates of could-be gears
+        mayGearCoords :: [Coord]
         mayGearCoords = M.keys $ M.filter (== '*') syms
-        adjacentCounts :: M.Map Coord [Int]
+        {-
+          Builds up a map from could-be gear coordinates to values of numbers
+          that are adjacent to them
+         -}
         adjacentCounts = M.fromListWith (<>) do
           n@(_, (v, _)) <- nums
           g <- mayGearCoords
           guard $ isAdjacent n g
           pure (g, [v])
-    answerShow
-      . getSum
-      . foldMap
-        ( \case
-            [a, b] -> Sum $ a * b
-            _ -> 0
-        )
-      $ M.elems
-        adjacentCounts
+      answerShow
+        . getSum
+        . foldMap
+          ( \case
+              [a, b] ->
+                -- only counts when the list contains exactly 2 elements.
+                Sum $ a * b
+              _ -> 0
+          )
+        $ adjacentCounts