Day 13

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

Day13/puzzle2.hs

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+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