From 9e245fe007355f726f3af5ecf843f1a051e72fb3 Mon Sep 17 00:00:00 2001
From: Daniel Lin <ephemient@gmail.com>
Date: Sat, 14 Dec 2024 10:28:43 -0500
Subject: [PATCH] Print the final position for reference

---
 hs/src/Day14.hs | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/hs/src/Day14.hs b/hs/src/Day14.hs
index 1037de22..f80eac39 100644
--- a/hs/src/Day14.hs
+++ b/hs/src/Day14.hs
@@ -7,6 +7,7 @@ module Day14 (part1, part1', part2) where
 
 import Common (groupConsecutiveBy)
 import Control.Monad (join, liftM2)
+import Data.Char (intToDigit)
 import Data.Map qualified as Map (findWithDefault)
 import Data.Map.Strict qualified as Map (fromListWith)
 import Data.Ord (Down (Down))
@@ -14,6 +15,7 @@ import Data.Set qualified as Set (fromList, toList)
 import Data.String (IsString)
 import Data.Text (Text)
 import Data.Void (Void)
+import Debug.Trace (traceM)
 import Text.Megaparsec (MonadParsec, ParseErrorBundle, Stream (Token, Tokens), parse, sepEndBy1)
 import Text.Megaparsec.Char (char, newline, string)
 import Text.Megaparsec.Char.Lexer qualified as L (decimal, signed)
@@ -44,16 +46,30 @@ part1' width height input = do
 part2 :: Text -> Either (ParseErrorBundle Text Void) Int
 part2 input = do
   robots <- parse parser "" input
-  pure . snd . minimum $
-    [ (Down $ maximum $ map length verticalLines, t)
-    | t <- [0 .. lcm width height - 1],
-      let verticalLines =
-            groupConsecutiveBy isLine . Set.toList . Set.fromList $
-              [ ((y0 + vy * t) `mod` height, (x0 + vx * t) `mod` width)
-              | ((x0, y0), (vx, vy)) <- robots
-              ]
-          isLine (y0, x0) (y1, x1) = y0 == y1 && x0 + 1 == x1
-    ]
+  let (_, bestTime) =
+        minimum
+          [ (Down $ maximum $ map length verticalLines, t)
+          | t <- [0 .. lcm width height - 1],
+            let verticalLines =
+                  groupConsecutiveBy isLine . Set.toList . Set.fromList $
+                    [ ((y0 + vy * t) `mod` height, (x0 + vx * t) `mod` width)
+                    | ((x0, y0), (vx, vy)) <- robots
+                    ]
+                isLine (y0, x0) (y1, x1) = y0 == y1 && x0 + 1 == x1
+          ]
+      positions =
+        Map.fromListWith (+) $
+          [ (((x0 + vx * bestTime) `mod` width, (y0 + vy * bestTime) `mod` height), 1)
+          | ((x0, y0), (vx, vy)) <- robots
+          ]
+      line y =
+        [ case Map.findWithDefault 0 (x, y) positions of
+            0 -> '.'
+            n -> if n < 10 then intToDigit n else '+'
+        | x <- [0 .. width - 1]
+        ]
+  mapM_ (traceM . line) [0 .. height - 1]
+  pure bestTime
   where
     width = 101
     height = 103