1 files changed, 67 insertions, 0 deletions
diff --git a/09_mirage_maintenance/mirage_maintenance.rs b/09_mirage_maintenance/mirage_maintenance.rs
new file mode 100644
index 0000000..204f157
--- /dev/null
+++ b/09_mirage_maintenance/mirage_maintenance.rs
@@ -0,0 +1,67 @@
+pub struct Measurement(Vec<i64>);
+
+impl From<&str> for Measurement {
+	fn from(value: &str) -> Self {
+		Self(value.split(' ').map(|x| x.parse::<i64>().unwrap()).collect())
+	}
+}
+
+impl Measurement {
+	fn differentiate(&self) -> Vec<Vec<i64>> {
+		let mut table = Vec::new();
+		table.push(self.0.clone());
+
+		loop {
+			let last = table.last().unwrap();
+			let mut new = Vec::new();
+			for i in 1..last.len() {
+				new.push(last[i] - last[i-1])
+			}
+			if new.iter().all(|x| x == &0) { break }
+			table.push(new);
+		}
+
+		table
+	}
+
+	pub fn predict(&self) -> i64 {
+		let table = self.differentiate();
+		let mut last_delta = 0;
+		for layer in table.iter().rev() {
+			last_delta += *layer.last().unwrap();
+		}
+		last_delta
+	}
+
+	pub fn predict_back(&self) -> i64 {
+		let table = self.differentiate();
+		let mut last_delta = 0;
+		for layer in table.iter().rev() {
+			last_delta = *layer.first().unwrap() - last_delta;
+		}
+		last_delta
+	}
+}
+
+
+fn main() {
+	let fname = match std::env::args().nth(1) {
+		None => return eprintln!("no input file given"),
+		Some(x) => x
+	};
+
+	let part_two = std::env::args().any(|x| x == "--part-two");
+
+	let content = std::fs::read_to_string(fname).unwrap();
+
+	let prediction_sum : i64 = content.lines()
+		.map(Measurement::from)
+		.map(|m| if part_two { m.predict_back() } else { m.predict() })
+		.sum();
+
+	println!(
+		"{} predictions sum: {}",
+		if part_two { "backward" } else { "forward" },
+		prediction_sum
+	);
+}