From 7cc43b607dcef1958edba80313c0ffdaea5f3aa2 Mon Sep 17 00:00:00 2001
From: Daniele Fucini <dfucini@gmail.com>
Date: Fri, 13 Dec 2024 21:46:35 +0100
Subject: [PATCH] Day 13

---
 Day13/puzzle1.hs | 31 +++++++++++++++++++++++++++++++
 Day13/puzzle2.hs | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 Day13/puzzle1.hs
 create mode 100644 Day13/puzzle2.hs

diff --git a/Day13/puzzle1.hs b/Day13/puzzle1.hs
new file mode 100644
index 0000000..76eec76
--- /dev/null
+++ b/Day13/puzzle1.hs
@@ -0,0 +1,31 @@
+import Data.Char (isDigit)
+import Data.List.Split (splitOn, chunksOf)
+import Data.Matrix (Matrix, fromLists, toList, rref, zero)
+import Data.Either (fromRight)
+import Data.Maybe (mapMaybe)
+
+isAlmostInt :: (RealFrac a) => a -> Bool
+isAlmostInt x = let diff = x - fromInteger (round x)
+                in  abs diff < 0.000001
+
+getMatrix :: (Read a) => String -> Matrix a
+getMatrix s = let nValues = map (map read . splitOn ",") . splitOn ":" . drop 1 $ filter (\x -> isDigit x || x == ',' || x == ':') s
+                  eq1 = map head nValues
+                  eq2 = map last nValues
+              in  fromLists [eq1, eq2]
+
+solve :: (RealFrac a) => Matrix a -> Maybe [a]
+solve eqSystem = let rowEchelonList = toList . fromRight (zero 1 1) $ rref eqSystem
+                     solutions = [ rowEchelonList !! 2, rowEchelonList !! 5 ]
+                 in  if all isAlmostInt solutions
+                        then Just solutions
+                     else Nothing
+
+cost :: [Int] -> Int
+cost [x, y] = 3 * x + y
+
+main = do
+    contents <- map concat . chunksOf 4 . lines <$> readFile "day13.txt"
+    let eqSystems = map getMatrix contents
+        solutions = (map . map) round $ mapMaybe solve eqSystems
+    print . sum $ map cost solutions
diff --git a/Day13/puzzle2.hs b/Day13/puzzle2.hs
new file mode 100644
index 0000000..690ca9b
--- /dev/null
+++ b/Day13/puzzle2.hs
@@ -0,0 +1,34 @@
+import Data.Char (isDigit)
+import Data.List.Split (splitOn, chunksOf)
+import Data.Matrix (Matrix, fromLists, toList, rref, zero)
+import Data.Either (fromRight)
+import Data.Maybe (mapMaybe)
+
+isAlmostInt :: (RealFrac a) => a -> Bool
+isAlmostInt x = let diff = x - fromInteger (round x)
+                in  abs diff < 0.001
+
+multRes :: (Num a) => [a] -> [a]
+multRes [x, y, z] = [x, y, z + 10000000000000]
+
+getMatrix :: (Num a, Read a) => String -> Matrix a
+getMatrix s = let nValues = map (map read . splitOn ",") . splitOn ":" . drop 1 $ filter (\x -> isDigit x || x == ',' || x == ':') s
+                  eq1 = multRes $ map head nValues
+                  eq2 = multRes $ map last nValues
+              in  fromLists [eq1, eq2]
+
+solve :: (RealFrac a) => Matrix a -> Maybe [a]
+solve eqSystem = let rowEchelonList = toList . fromRight (zero 1 1) $ rref eqSystem
+                     solutions = [ rowEchelonList !! 2, rowEchelonList !! 5 ]
+                 in  if all isAlmostInt solutions
+                        then Just solutions
+                     else Nothing
+
+cost :: [Int] -> Int
+cost [x, y] = 3 * x + y
+
+main = do
+    contents <- map concat . chunksOf 4 . lines <$> readFile "day13.txt"
+    let eqSystems = map getMatrix contents
+        solutions = (map . map) round $ mapMaybe solve eqSystems
+    print . sum $ map cost solutions