[2023] Complete day 9

README.md

@@ -13,6 +13,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 06: Wait For It](aoc_2023/src/day_06.rs)
 - [Day 07: Camel Cards](aoc_2023/src/day_07.rs)
 - [Day 08: Haunted Wasteland](aoc_2023/src/day_08.rs)
+- [Day 09: Mirage Maintenance](aoc_2023/src/day_09.rs)
 <!-- MARKER -->
 
 ## [2022](https://adventofcode.com/2022) [![aoc_2022](https://github.com/Basicprogrammer10/advent-of-code/actions/workflows/aoc_2022.yml/badge.svg)](https://github.com/Basicprogrammer10/advent-of-code/actions/workflows/aoc_2022.yml)

aoc_2023/src/day_09.rs

@@ -0,0 +1,98 @@
+use common::{Answer, Solution};
+
+pub struct Day09;
+
+impl Solution for Day09 {
+    fn name(&self) -> &'static str {
+        "Mirage Maintenance"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        parse(input)
+            .iter()
+            .map(Sequence::predict)
+            .sum::<i64>()
+            .into()
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        parse(input)
+            .iter()
+            .map(Sequence::predict_back)
+            .sum::<i64>()
+            .into()
+    }
+}
+
+struct Sequence {
+    values: Vec<i64>,
+}
+
+fn parse(input: &str) -> Vec<Sequence> {
+    let mut out = Vec::new();
+
+    for line in input.lines() {
+        let values = line
+            .split_whitespace()
+            .map(|v| v.parse().unwrap())
+            .collect();
+        out.push(Sequence { values });
+    }
+
+    out
+}
+
+impl Sequence {
+    fn derive(&self, rev: bool) -> Vec<Vec<i64>> {
+        let mut derived = vec![self.values.clone()];
+
+        while !derived.last().unwrap().iter().all(|&x| x == 0) {
+            let last = derived.last().unwrap();
+            let mut next = Vec::new();
+
+            for i in 1..last.len() {
+                if rev {
+                    next.push(last[i - 1] - last[i]);
+                } else {
+                    next.push(last[i] - last[i - 1]);
+                }
+            }
+
+            derived.push(next);
+        }
+
+        derived
+    }
+
+    fn predict(&self) -> i64 {
+        self.derive(false).iter().filter_map(|v| v.last()).sum()
+    }
+
+    fn predict_back(&self) -> i64 {
+        self.derive(true).iter().rev().map(|v| v[0]).sum()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use common::Solution;
+    use indoc::indoc;
+
+    use super::Day09;
+
+    const CASE: &str = indoc! {"
+        0 3 6 9 12 15
+        1 3 6 10 15 21
+        10 13 16 21 30 45
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day09.part_a(CASE), 114.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day09.part_b(CASE), 2.into());
+    }
+}

aoc_2023/src/lib.rs

@@ -10,6 +10,7 @@ mod day_05;
 mod day_06;
 mod day_07;
 mod day_08;
+mod day_09;
 // [import_marker]
 
 #[rustfmt::skip]
@@ -22,5 +23,6 @@ pub const ALL: &[&dyn Solution] = &[
     &day_06::Day06,
     &day_07::Day07,
     &day_08::Day08,
+    &day_09::Day09,
     // [list_marker]
 ];