day 9

README.md

@@ -24,16 +24,17 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 
 | Day | Part 1 | Part 2 |
 | :---: | :---: | :---:  |
-| [Day 1](./src/bin/01.rs) | `33.6µs` | `36.1µs` |
-| [Day 2](./src/bin/02.rs) | `42.5µs` | `41.8µs` |
-| [Day 3](./src/bin/03.rs) | `84.6µs` | `99.7µs` |
-| [Day 4](./src/bin/04.rs) | `48.6µs` | `51.3µs` |
-| [Day 5](./src/bin/05.rs) | `20.7µs` | `24.3µs` |
-| [Day 6](./src/bin/06.rs) | `202.0ns` | `102.0ns` |
-| [Day 7](./src/bin/07.rs) | `95.9µs` | `92.6µs` |
-| [Day 8](./src/bin/08.rs) | `74.5µs` | `159.3µs` |
-
-**Total: 0.91ms**
+| [Day 1](./src/bin/01.rs) | `33.3µs` | `35.8µs` |
+| [Day 2](./src/bin/02.rs) | `42.5µs` | `40.5µs` |
+| [Day 3](./src/bin/03.rs) | `82.7µs` | `97.8µs` |
+| [Day 4](./src/bin/04.rs) | `48.2µs` | `49.5µs` |
+| [Day 5](./src/bin/05.rs) | `20.4µs` | `24.4µs` |
+| [Day 6](./src/bin/06.rs) | `203.0ns` | `102.0ns` |
+| [Day 7](./src/bin/07.rs) | `93.9µs` | `94.0µs` |
+| [Day 8](./src/bin/08.rs) | `73.0µs` | `160.4µs` |
+| [Day 9](./src/bin/09.rs) | `58.0µs` | `57.5µs` |
+
+**Total: 1.01ms**
 <!--- benchmarking table --->
 
 ---

data/examples/09.txt

@@ -0,0 +1,3 @@
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45

src/bin/09.rs

@@ -0,0 +1,77 @@
+use rayon::{iter::ParallelIterator, str::ParallelString};
+
+advent_of_code::solution!(9);
+
+pub fn part_one(input: &str) -> Option<i32> {
+    Some(
+        input
+            .par_lines()
+            .map(|line| {
+                let nums = line
+                    .split_whitespace()
+                    .map(|ch| ch.parse::<i32>().expect("should be a number"))
+                    .collect::<Vec<_>>();
+                find_next(nums)
+            })
+            .sum(),
+    )
+}
+
+pub fn part_two(input: &str) -> Option<i32> {
+    Some(
+        input
+            .par_lines()
+            .map(|line| {
+                let nums = line
+                    .split_whitespace()
+                    .rev()
+                    .map(|ch| ch.parse::<i32>().expect("should be a number"))
+                    .collect::<Vec<_>>();
+                find_next(nums)
+            })
+            .sum(),
+    )
+}
+
+fn find_next(input: Vec<i32>) -> i32 {
+    let Some(&last_value) = input.last() else {
+        return 0;
+    };
+    let mut differences = input;
+    let mut last_difference_sum = 0;
+    while differences.len() > 1 {
+        let mut all_zeros = true;
+        for i in 1..differences.len() {
+            let difference = differences[i] - differences[i - 1];
+            if difference != 0 {
+                all_zeros = false;
+            }
+            differences[i - 1] = difference;
+            if i == differences.len() - 1 {
+                last_difference_sum += difference;
+            }
+        }
+        if all_zeros {
+            break;
+        }
+        differences.pop();
+    }
+    last_value + last_difference_sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(114));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(2));
+    }
+}