day 9

2 files changed, 51 insertions, 0 deletions

diff --git a/src/bin/2023/day9.rs b/src/bin/2023/day9.rs
new file mode 100644
index 0000000..d04c209
--- /dev/null
+++ b/src/bin/2023/day9.rs
@@ -0,0 +1,49 @@
+#![allow(dead_code)]
+#![allow(unused_variables)]
+
+use advent_of_code::prelude::*;
+
+fn calculate_next(v: Vec<i64>) -> i64 {
+    if v.iter().all(|n| *n == 0) {
+        return 0;
+    }
+    calculate_next((1..v.len()).map(|i| v[i] - v[i - 1]).collect())
+        + v[v.len() - 1]
+}
+
+fn calculate_prev(v: Vec<i64>) -> i64 {
+    if v.iter().all(|n| *n == 0) {
+        return 0;
+    }
+    v[0] - calculate_prev((1..v.len()).map(|i| v[i] - v[i - 1]).collect())
+}
+
+pub fn parse(fh: File) -> Result<Vec<Vec<i64>>> {
+    Ok(parse::raw_lines(fh)
+        .map(|line| {
+            line.split_whitespace()
+                .map(|s| s.parse().unwrap())
+                .collect()
+        })
+        .collect())
+}
+
+pub fn part1(report: Vec<Vec<i64>>) -> Result<i64> {
+    Ok(report.into_iter().map(calculate_next).sum())
+}
+
+pub fn part2(report: Vec<Vec<i64>>) -> Result<i64> {
+    Ok(report.into_iter().map(calculate_prev).sum())
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2023, 9).unwrap()).unwrap()).unwrap(),
+        0
+    );
+    assert_eq!(
+        part2(parse(parse::data(2023, 9).unwrap()).unwrap()).unwrap(),
+        0
+    );
+}
diff --git a/src/bin/2023/main.rs b/src/bin/2023/main.rs
index 569886c..2a5c575 100644
--- a/src/bin/2023/main.rs
+++ b/src/bin/2023/main.rs
@@ -19,6 +19,7 @@ mod day5;
 mod day6;
 mod day7;
 mod day8;
+mod day9;
 // NEXT MOD
 
 #[paw::main]
@@ -33,6 +34,7 @@ fn main(opt: Opt) -> Result<()> {
         6 => advent_of_code::day!(2023, opt.day, opt.puzzle, day6),
         7 => advent_of_code::day!(2023, opt.day, opt.puzzle, day7),
         8 => advent_of_code::day!(2023, opt.day, opt.puzzle, day8),
+        9 => advent_of_code::day!(2023, opt.day, opt.puzzle, day9),
         // NEXT PART
         _ => panic!("unknown day {}", opt.day),
     }