From d94a6b3e6012b34db9470639d95a8223e4275cc5 Mon Sep 17 00:00:00 2001
From: dobiadi <dobi@ktk.bme.hu>
Date: Sat, 9 Dec 2023 22:19:40 +0100
Subject: [PATCH] Day9 Rust

---
 day9/rust/.gitignore  |  1 +
 day9/rust/Cargo.lock  |  7 +++++++
 day9/rust/Cargo.toml  |  8 ++++++++
 day9/rust/src/main.rs | 37 +++++++++++++++++++++++++++++++++++++
 4 files changed, 53 insertions(+)
 create mode 100644 day9/rust/.gitignore
 create mode 100644 day9/rust/Cargo.lock
 create mode 100644 day9/rust/Cargo.toml
 create mode 100644 day9/rust/src/main.rs

diff --git a/day9/rust/.gitignore b/day9/rust/.gitignore
new file mode 100644
index 0000000..eb5a316
--- /dev/null
+++ b/day9/rust/.gitignore
@@ -0,0 +1 @@
+target
diff --git a/day9/rust/Cargo.lock b/day9/rust/Cargo.lock
new file mode 100644
index 0000000..b21cc6a
--- /dev/null
+++ b/day9/rust/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rust"
+version = "0.1.0"
diff --git a/day9/rust/Cargo.toml b/day9/rust/Cargo.toml
new file mode 100644
index 0000000..1ec6963
--- /dev/null
+++ b/day9/rust/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "rust"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day9/rust/src/main.rs b/day9/rust/src/main.rs
new file mode 100644
index 0000000..f07ed10
--- /dev/null
+++ b/day9/rust/src/main.rs
@@ -0,0 +1,37 @@
+enum Direction {
+    Forward,
+    Backward,
+}
+
+fn main() {
+    let stdin = std::io::stdin();
+
+    let mut part1 = 0;
+    let mut part2 = 0;
+
+    for line in stdin.lines() {
+        let line = line.unwrap();
+
+        let history = line.split(" ").map(|e| e.parse().unwrap()).collect();
+
+        part1 += extrapolate(&history, Direction::Forward);
+        part2 += extrapolate(&history, Direction::Backward);
+    }
+
+    println!("{}", part1);
+    println!("{}", part2);
+}
+
+fn extrapolate(history: &Vec<isize>, direction: Direction) -> isize {
+    if history.iter().all(|e| *e == 0) {
+        return 0;
+    }
+
+    let new_history = history.windows(2).map(|pair| pair[1] - pair[0]).collect();
+
+    if let Direction::Forward = direction {
+        return history.last().unwrap() + extrapolate(&new_history, direction);
+    }
+
+    return history[0] - extrapolate(&new_history, direction);
+}