From b26eca34cd939200e4815bcf7f7031c43ea48641 Mon Sep 17 00:00:00 2001
From: Julien Dessaux
Date: Tue, 19 Nov 2024 00:31:01 +0100
Subject: 2023-24 part 1 in haskell

---
 2023/24-Never_Tell_Me_The_Odds/first.hs | 81 +++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 2023/24-Never_Tell_Me_The_Odds/first.hs

(limited to '2023/24-Never_Tell_Me_The_Odds/first.hs')

diff --git a/2023/24-Never_Tell_Me_The_Odds/first.hs b/2023/24-Never_Tell_Me_The_Odds/first.hs
new file mode 100644
index 0000000..0964c12
--- /dev/null
+++ b/2023/24-Never_Tell_Me_The_Odds/first.hs
@@ -0,0 +1,81 @@
+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import           Control.Applicative.Permutations
+import           Control.Monad                    (void, when)
+import qualified Data.Char                        as C
+import           Data.Either
+import           Data.Functor
+import qualified Data.Heap                        as H
+import qualified Data.List                        as L
+import qualified Data.Map                         as M
+import           Data.Maybe
+import           Data.Ratio
+import qualified Data.Set                         as S
+import qualified Data.Vector                      as V
+import qualified Data.Vector.Unboxed              as VU
+import           Data.Void                        (Void)
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+
+import           Debug.Trace
+
+exampleExpectedOutput = 2
+
+type Hail = (Rational, Rational, Rational, Rational, Rational, Rational)
+type Input = [Hail]
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Integer
+parseNumber = read <$> some (char '-' <|> digitChar) <* optional (char ',') <* optional hspace <* optional (char '@' <* hspace)
+
+parseHail :: Parser Hail
+parseHail = (,,,,,) <$> (fromInteger <$> parseNumber)
+                    <*> (fromInteger <$> parseNumber)
+                    <*> (fromInteger <$> parseNumber)
+                    <*> (fromInteger <$> parseNumber)
+                    <*> (fromInteger <$> parseNumber)
+                    <*> (fromInteger <$> parseNumber)
+
+parseInput' :: Parser Input
+parseInput' = some (parseHail <* eol) <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle  -> error $ errorBundlePretty bundle
+    Right input' -> return input'
+
+compute :: Rational -> Rational -> Input -> Int
+compute mini maxi = compute'
+  where
+    compute' :: Input -> Int
+    compute' (_:[]) = 0
+    compute' ((x1, y1, _, a1, b1, _):hs) = L.foldl' computeOne 0 hs + compute' hs
+      where
+        (x2, y2) = (x1 + a1, y1 + b1)
+        computeOne :: Int -> Hail -> Int
+        computeOne acc (x3, y3, _, a3, b3, _) | valid = acc + 1
+                                              | otherwise = acc
+          where
+            valid | denominator == 0 || t < 0 || u < 0 = False
+                  | x >= mini && x <= maxi && y >= mini && y <= maxi = True
+                  | otherwise = False
+            (x4, y4) = (x3 + a3, y3 + b3)
+            denominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4)
+            a = x1 * y2 - y1 * x2
+            b = x3 * y4 - y3 * x4
+            numeratorX = b * a1 - a * a3
+            numeratorY = b * b1 - a * b3
+            (x, y) = (numeratorX / denominator, numeratorY / denominator)
+            (t, u) = ((x - x1) / a1, (x - x3) / a3)
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute 7 27 example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute 200000000000000 400000000000000 input
-- 
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