solve: day10

Author: tom-anders

Cargo.toml

@@ -2,7 +2,7 @@
 resolver = "2"
 members = [
     "utils",
-    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9",
+    "aoc_derive", "day1", "day2", "day3", "day4", "day5", "day6", "day7", "day8", "day9", "day10",
 ]
 
 [workspace.dependencies]

day10/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "day10"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aoc_derive.path = '../aoc_derive'
+utils.path = '../utils'
+derive_more.workspace = true
+itertools.workspace = true
+lazy-regex.workspace = true
+parse-display.workspace = true
+rayon.workspace = true
+regex.workspace = true
+num.workspace = true
+
+[dev-dependencies]
+pretty_assertions.workspace = true

day10/src/main.rs

@@ -0,0 +1,61 @@
+use aoc_derive::aoc_main;
+use grid::Grid;
+use itertools::Itertools;
+use math::Vec2D;
+use utils::*;
+
+fn hiking_paths(pos: Vec2D, map: &Grid<usize>) -> Vec<Vec2D> {
+    if map[pos] == 9 {
+        return vec![pos];
+    }
+
+    map.orthogonal_neighbors(&pos)
+        .filter(|&neighbor| map[neighbor] == map[pos] + 1)
+        .flat_map(|pos| hiking_paths(pos, map))
+        .collect_vec()
+}
+
+#[aoc_main]
+fn solve(input: Input) -> impl Into<Solution> {
+    let map = input.number_grid();
+
+    map.iter().filter_map(|(pos, &val)| (val == 0).then_some(pos)).fold(
+        (0, 0),
+        |(part1, part2), trailhead| {
+            let score = hiking_paths(trailhead, &map);
+            (part1 + score.iter().unique().count(), part2 + score.len())
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_examples() {
+        use utils::assert_example;
+        assert_example!(
+            r#"0123
+1234
+8765
+9876
+                "#,
+            1
+        );
+
+        assert_example!(
+            r#"
+            89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732
+            "#,
+            36,
+            81
+        );
+    }
+}