From cb79c63bb236bdc583ad21c53f3f1e74a0c5b599 Mon Sep 17 00:00:00 2001
From: RhiobeT <rhiobet@gmail.com>
Date: Sat, 9 Dec 2023 10:04:40 +0100
Subject: [PATCH] Day 9

---
 advent-of-code-2023.cabal |  8 ++++++++
 day09/Commons.hs          | 26 ++++++++++++++++++++++++++
 day09/Main.hs             | 12 ++++++++++++
 day09/Part1.hs            |  7 +++++++
 day09/Part2.hs            |  7 +++++++
 5 files changed, 60 insertions(+)
 create mode 100644 day09/Commons.hs
 create mode 100644 day09/Main.hs
 create mode 100644 day09/Part1.hs
 create mode 100644 day09/Part2.hs

diff --git a/advent-of-code-2023.cabal b/advent-of-code-2023.cabal
index dfc04e5..7bec955 100644
--- a/advent-of-code-2023.cabal
+++ b/advent-of-code-2023.cabal
@@ -68,3 +68,11 @@ executable day08
     build-depends:    base ^>=4.15.1.0, hashable, unordered-containers
     hs-source-dirs:   day08
     default-language: Haskell2010
+
+executable day09
+    main-is:          Main.hs
+    other-modules:    Commons Part1 Part2
+
+    build-depends:    base ^>=4.15.1.0, MissingH
+    hs-source-dirs:   day09
+    default-language: Haskell2010
diff --git a/day09/Commons.hs b/day09/Commons.hs
new file mode 100644
index 0000000..f4dbccb
--- /dev/null
+++ b/day09/Commons.hs
@@ -0,0 +1,26 @@
+module Commons where
+
+import GHC.IO.Handle (isEOF)
+import Data.List.Utils (split)
+
+
+type History = [Int]
+
+
+parse :: IO [History]
+parse = do done <- isEOF
+           if done
+              then return []
+              else do line <- getLine
+                      let history = map read $ split " " line
+                      otherHistories <- parse
+                      return $ history: otherHistories
+
+
+getDifferences :: History -> History
+getDifferences [h] = []
+getDifferences (h1: h2: t) = h1 - h2: getDifferences (h2: t)
+
+getNextValue :: History -> Int
+getNextValue (0: 0: _) = 0
+getNextValue (h: t) = h + (getNextValue . getDifferences) (h: t)
diff --git a/day09/Main.hs b/day09/Main.hs
new file mode 100644
index 0000000..26432f9
--- /dev/null
+++ b/day09/Main.hs
@@ -0,0 +1,12 @@
+module Main where
+
+import Commons
+import qualified Part1
+import qualified Part2
+
+
+main = do histories <- parse
+          let part1Res = sum $ Part1.getNextValues histories
+          print part1Res
+          let part2Res = sum $ Part2.getNextValues histories
+          print part2Res
diff --git a/day09/Part1.hs b/day09/Part1.hs
new file mode 100644
index 0000000..10babc2
--- /dev/null
+++ b/day09/Part1.hs
@@ -0,0 +1,7 @@
+module Part1 where
+
+import Commons
+
+
+getNextValues :: [History] -> [Int]
+getNextValues = map $ getNextValue . reverse
diff --git a/day09/Part2.hs b/day09/Part2.hs
new file mode 100644
index 0000000..45bc989
--- /dev/null
+++ b/day09/Part2.hs
@@ -0,0 +1,7 @@
+module Part2 where
+
+import Commons
+
+
+getNextValues :: [History] -> [Int]
+getNextValues = map getNextValue