Day 9 done.

1 files changed, 83 insertions, 0 deletions

diff --git a/2023/Rust/src/day9.rs b/2023/Rust/src/day9.rs
new file mode 100644
index 0000000..ed8d63e
--- /dev/null
+++ b/2023/Rust/src/day9.rs
@@ -0,0 +1,83 @@
+type History = Vec<i64>;
+
+#[derive(Debug)]
+struct Report {
+    histories: Vec<History>,
+}
+
+impl From<&str> for Report {
+    fn from(report: &str) -> Self {
+        Self {
+            histories: report
+                .lines()
+                .map(|line| {
+                    line.split_whitespace()
+                        .map(|num| num.parse::<i64>().unwrap())
+                        .collect::<History>()
+                })
+                .collect::<Vec<History>>(),
+        }
+    }
+}
+
+fn solve_part_one(data: &str) -> u64 {
+    let report = Report::from(data);
+    let mut ans = 0;
+    for history in report.histories.iter() {
+        let mut differences = vec![];
+        differences.push(history.clone());
+        while !differences.last().unwrap().iter().all(|&x| x == 0) {
+            differences.push(
+                differences
+                    .last()
+                    .unwrap()
+                    .windows(2)
+                    .map(|window| window[1] - window[0])
+                    .collect::<Vec<_>>(),
+            )
+        }
+
+        for i in (0..differences.len() - 2).rev() {
+            let last_last = differences[i + 1].last().unwrap() + differences[i].last().unwrap();
+            differences[i].push(last_last);
+        }
+        ans += differences.first().unwrap().last().unwrap();
+    }
+    ans as u64
+}
+
+fn solve_part_two(data: &str) -> u64 {
+    let report = Report::from(data);
+    let mut ans = 0;
+    for history in report.histories.iter() {
+        let mut differences = vec![];
+        differences.push(history.clone());
+        while !differences.last().unwrap().iter().all(|&x| x == 0) {
+            differences.push(
+                differences
+                    .last()
+                    .unwrap()
+                    .windows(2)
+                    .map(|window| window[1] - window[0])
+                    .collect::<Vec<_>>(),
+            )
+        }
+
+        for i in (0..differences.len() - 2).rev() {
+            let first_first = differences[i].first().unwrap() - differences[i + 1].first().unwrap();
+            differences[i].insert(0, first_first);
+        }
+        ans += differences.first().unwrap().first().unwrap();
+    }
+    ans as u64
+}
+
+fn main() {
+    let test_1 = include_str!("../input/day9_1.test");
+    let test_2 = include_str!("../input/day9_2.test");
+    let prod = include_str!("../input/day9.prod");
+    println!("part_1 test: {:?}", solve_part_one(test_1));
+    println!("part_1 prod {:?}", solve_part_one(prod));
+    println!("part_2 test: {:?}", solve_part_two(test_2));
+    println!("part_2 prod {:?}", solve_part_two(prod));
+}