From 7a2a388e846d27c03918a4bb231a442588831b8c Mon Sep 17 00:00:00 2001
From: Daniele Fucini <dfucini@gmail.com>
Date: Tue, 9 Dec 2025 17:11:20 +0100
Subject: [PATCH] Add Day 8, Puzzle 2 solution

---
 src/Day08.hs | 23 +++++++++++++++++++++++
 src/Main.hs  |  5 ++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/Day08.hs b/src/Day08.hs
index 52aec0c..bcc022c 100644
--- a/src/Day08.hs
+++ b/src/Day08.hs
@@ -2,6 +2,7 @@
 
 module Day08
   ( day08_1,
+    day08_2,
   )
 where
 
@@ -45,6 +46,17 @@ buildCircuits [] circuits _ = circuits
 buildCircuits _ circuits 0 = circuits
 buildCircuits ((x, y, _) : xs) circuits n = buildCircuits xs (mergeCircuits x y circuits) (n - 1)
 
+findLastPoint :: [(Point, Point, Float)] -> [[Point]] -> (Point, Point)
+findLastPoint [] _ = ((0, 0, 0), (0, 0, 0))
+findLastPoint ((x, y, _) : xs) circuits =
+  let circuits' = mergeCircuits x y circuits
+   in if length circuits' == 1
+        then (x, y)
+        else findLastPoint xs circuits'
+
+getX :: Point -> Int
+getX (x, _, _) = x
+
 parseInput :: IO [Point]
 parseInput = do
   input <- lines <$> readFile "input/day8.txt"
@@ -61,3 +73,14 @@ day08_1 = do
   putStrLn $
     "Day 8, Puzzle 1 solution: "
       ++ show result
+
+day08_2 :: IO ()
+day08_2 = do
+  points <- parseInput
+  let distances = getSortedDistances points
+      points' = map (: []) points
+      lastPoints = findLastPoint distances points'
+      result = getX (fst lastPoints) * getX (snd lastPoints)
+  putStrLn $
+    "Day 8, Puzzle 2 solution: "
+      ++ show result
diff --git a/src/Main.hs b/src/Main.hs
index 0d50156..4eab540 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -7,7 +7,7 @@ import Day04 (day04_1, day04_2)
 import Day05 (day05_1, day05_2)
 import Day06 (day06_1, day06_2)
 import Day07 (day07_1)
-import Day08 (day08_1)
+import Day08 (day08_1, day08_2)
 import System.Environment (getArgs)
 
 main :: IO ()
@@ -48,8 +48,10 @@ main = do
     "7" : _ -> do
       day07_1
     "8" : "1" : _ -> day08_1
+    "8" : "2" : _ -> day08_2
     "8" : _ -> do
       day08_1
+      day08_2
     "all" : _ -> do
       day01_1
       day01_2
@@ -65,4 +67,5 @@ main = do
       day06_2
       day07_1
       day08_1
+      day08_2
     _ -> error "Not implemented"