Merge pull request #224 from paulcacheux/day9-2023

Day9 2023

inputs/2023/day9_test.txt

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

results/2023.json

@@ -38,5 +38,10 @@
         "day": 8,
         "part1": "13771",
         "part2": "13129439557681"
+    },
+    {
+        "day": 9,
+        "part1": "1702218515",
+        "part2": "925"
     }
 ]

src/aoc2023/day9.rs

@@ -0,0 +1,70 @@
+use crate::aoc2023::Aoc2023;
+use crate::traits::days::Day9;
+use crate::traits::ParseInput;
+use crate::traits::Solution;
+
+impl ParseInput<Day9> for Aoc2023 {
+    type Parsed = Vec<Vec<i32>>;
+
+    fn parse_input(input: &str) -> Self::Parsed {
+        input
+            .lines()
+            .map(|line| {
+                line.split_ascii_whitespace()
+                    .map(|value| value.parse().unwrap())
+                    .collect()
+            })
+            .collect()
+    }
+}
+
+impl Solution<Day9> for Aoc2023 {
+    type Part1Output = i32;
+    type Part2Output = i32;
+
+    fn part1(input: &Vec<Vec<i32>>) -> i32 {
+        solve(input, false)
+    }
+
+    fn part2(input: &Vec<Vec<i32>>) -> i32 {
+        solve(input, true)
+    }
+}
+
+fn solve(input: &Vec<Vec<i32>>, part2: bool) -> i32 {
+    let mut sum = 0;
+    for line in input {
+        let mut history = Vec::new();
+        let mut current = line.clone();
+
+        while !current.iter().all(|&v| v == 0) {
+            history.push(
+                *(if part2 {
+                    current.first()
+                } else {
+                    current.last()
+                })
+                .unwrap(),
+            );
+
+            let mut next_line: Vec<i32> = Vec::with_capacity(current.len() - 1);
+            for [a, b] in current.array_windows() {
+                let delta = b - a;
+                next_line.push(delta);
+            }
+            current = next_line;
+        }
+
+        sum += history.into_iter().rev().fold(
+            0,
+            |acc, value| {
+                if part2 {
+                    value - acc
+                } else {
+                    value + acc
+                }
+            },
+        );
+    }
+    sum
+}

src/aoc2023/mod.rs

@@ -11,6 +11,7 @@ pub mod day5;
 pub mod day6;
 pub mod day7;
 pub mod day8;
+pub mod day9;
 
 pub fn run_solution_for_day(day: u32, input: &str, results: Option<Results>) -> Option<TimingData> {
     let r = results
@@ -26,6 +27,7 @@ pub fn run_solution_for_day(day: u32, input: &str, results: Option<Results>) ->
         6 => run::<Aoc2023, Day6>(input, r),
         7 => run::<Aoc2023, Day7>(input, r),
         8 => run::<Aoc2023, Day8>(input, r),
+        9 => run::<Aoc2023, Day9>(input, r),
         _ => return None,
     };
     Some(elapsed)