2024.10

2 files changed, 81 insertions, 0 deletions

diff --git a/2024_rust/src/bin/day10.rs b/2024_rust/src/bin/day10.rs
new file mode 100644
index 0000000..3c208bd
--- /dev/null
+++ b/2024_rust/src/bin/day10.rs
@@ -0,0 +1,68 @@
+use aoc2024::matrix;
+use std::collections::HashSet;
+
+static AROUND_DELTAS: [(isize, isize); 4] = [(-1, 0), (0, -1), (0, 1), (1, 0)];
+
+type Matrix = matrix::Matrix<u32>;
+type Trailhead = matrix::Pos;
+
+fn trailheads(m: &Matrix) -> Vec<Trailhead> {
+    let mut result: Vec<Trailhead> = vec![];
+    for i in 0..m.limit.0 {
+        for j in 0..m.limit.1 {
+            let pos = (i, j);
+            if m.get(pos) == &0 {
+                result.push(pos);
+            }
+        }
+    }
+    result
+}
+
+fn reachable(m: &Matrix, pos: matrix::Pos) -> HashSet<matrix::Pos> {
+    let height = m.get(pos);
+    AROUND_DELTAS
+        .iter()
+        .filter_map(|&d| m.pos_move(pos, d))
+        .filter(|&p| *m.get(p) == height + 1)
+        .collect()
+}
+
+fn score1(m: &Matrix, th: Trailhead) -> u32 {
+    let mut heads: HashSet<matrix::Pos> = HashSet::new();
+    heads.insert(th);
+    let mut height = 0;
+    while height < 9 {
+        heads = heads.into_iter().flat_map(|th| reachable(m, th)).collect();
+        height += 1;
+    }
+    heads.len() as u32
+}
+
+fn p1(input: &str) -> String {
+    let m: Matrix = matrix::Matrix::new(input, |c| c.to_digit(10).unwrap());
+    let result: u32 = trailheads(&m).iter().map(|&th| score1(&m, th)).sum();
+
+    result.to_string()
+}
+
+fn score2(m: &Matrix, th: Trailhead) -> u32 {
+    let mut heads: Vec<matrix::Pos> = vec![th];
+    let mut height = 0;
+    while height < 9 {
+        heads = heads.into_iter().flat_map(|th| reachable(m, th)).collect();
+        height += 1;
+    }
+    heads.len() as u32
+}
+
+fn p2(input: &str) -> String {
+    let m: Matrix = matrix::Matrix::new(input, |c| c.to_digit(10).unwrap());
+    let result: u32 = trailheads(&m).iter().map(|&th| score2(&m, th)).sum();
+
+    result.to_string()
+}
+
+fn main() {
+    aoc2024::run_day("10", Some(p1), Some(p2));
+}
diff --git a/2024_rust/src/lib.rs b/2024_rust/src/lib.rs
index c034fea..ea6f7d6 100644
--- a/2024_rust/src/lib.rs
+++ b/2024_rust/src/lib.rs
@@ -1,5 +1,6 @@
 pub mod matrix {
     pub type Pos = (usize, usize);
+    pub type PosDelta = (isize, isize);
 
     #[derive(Clone)]
     pub struct Matrix<T> {
@@ -27,6 +28,18 @@ pub mod matrix {
         pub fn set(&mut self, (x, y): Pos, dot: T) {
             self.dots[x][y] = dot;
         }
+
+        pub fn pos_move(&self, (x, y): Pos, (dx, dy): PosDelta) -> Option<Pos> {
+            let x2 = x as isize + dx;
+            if x2 < 0 || x2 >= self.limit.0 as isize {
+                return None;
+            }
+            let y2 = y as isize + dy;
+            if y2 < 0 || y2 >= self.limit.1 as isize {
+                return None;
+            }
+            Some((x2 as usize, y2 as usize))
+        }
     }
 
     use std::fmt;