Year 2024, Day 10

year2024/src/day10.rs

@@ -0,0 +1,82 @@
+use std::collections::{HashSet, VecDeque};
+
+use common::day::Day;
+use util::grid2d::{Coords, Grid2D};
+
+pub struct Day10 {}
+
+impl Day for Day10 {
+    fn star1(&self, input: &str) -> String {
+        let grid = Grid2D::new_by(input, |c| c.to_digit(10).unwrap() as u8).unwrap();
+        let score = grid
+            .filter(&[0])
+            .into_iter()
+            .map(|trailhead| trail_score(&grid, trailhead, false))
+            .sum::<usize>();
+        format!("{}", score)
+    }
+
+    fn star2(&self, input: &str) -> String {
+        let grid = Grid2D::new_by(input, |c| c.to_digit(10).unwrap() as u8).unwrap();
+        let rating = grid
+            .filter(&[0])
+            .into_iter()
+            .map(|trailhead| trail_score(&grid, trailhead, true))
+            .sum::<usize>();
+        format!("{}", rating)
+    }
+}
+
+fn trail_score(grid: &Grid2D<u8>, trailhead: Coords, all_paths: bool) -> usize {
+    let mut score = 0;
+    let mut frontier = VecDeque::new();
+    frontier.push_back(trailhead);
+    let mut visited = HashSet::new();
+    if !all_paths {
+        visited.insert(trailhead);
+    }
+
+    while let Some(pos) = frontier.pop_front() {
+        let pos_height = grid.at(&pos).unwrap();
+        for neighbor_pos in grid.neighbors_cardinal_coords(&pos) {
+            if let Some(neighbor_height) = grid.at(&neighbor_pos) {
+                if *neighbor_height == pos_height + 1 && (all_paths || visited.insert(neighbor_pos))
+                {
+                    if *neighbor_height == 9 {
+                        score += 1;
+                    } else {
+                        frontier.push_back(neighbor_pos);
+                    }
+                }
+            }
+        }
+    }
+
+    score
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = r#"89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732"#;
+
+    #[test]
+    fn star1() {
+        let d = Day10 {};
+        assert_eq!(d.star1(INPUT), "36");
+    }
+
+    #[test]
+    fn star2() {
+        let d = Day10 {};
+        assert_eq!(d.star2(INPUT), "81");
+    }
+}

year2024/src/lib.rs

@@ -10,6 +10,7 @@ mod day06;
 mod day07;
 mod day08;
 mod day09;
+mod day10;
 
 pub struct Year2024 {}
 
@@ -25,6 +26,7 @@ impl Year for Year2024 {
             7 => Some(Box::new(day07::Day07 {})),
             8 => Some(Box::new(day08::Day08 {})),
             9 => Some(Box::new(day09::Day09 {})),
+            10 => Some(Box::new(day10::Day10 {})),
             _ => None,
         }
     }