24-10-rs both

1 files changed, 52 insertions, 0 deletions

diff --git a/2024/10/rust/src/main.rs b/2024/10/rust/src/main.rs
new file mode 100644
index 0000000..b5b3825
--- /dev/null
+++ b/2024/10/rust/src/main.rs
@@ -0,0 +1,52 @@
+use std::collections::HashSet;
+use std::io;
+
+fn main() -> io::Result<()> {
+    let grid: Vec<Vec<u8>> = io::stdin()
+        .lines()
+        .flatten()
+        .map(|s| s.chars().map(|c| c.to_digit(10).unwrap() as u8).collect())
+        .collect();
+
+    let starts = grid
+        .iter()
+        .enumerate()
+        .flat_map(|(y, row)| row.iter().enumerate().map(move |(x, d)| (x, y, d)))
+        .filter_map(|(x, y, d)| (*d == 0).then_some((y, x)))
+        .collect::<Vec<_>>();
+
+    let silver: usize = starts.iter().map(|&s| trailheads(s, &grid, false)).sum();
+    let gold: usize = starts.iter().map(|&s| trailheads(s, &grid, true)).sum();
+
+    println!("silver: {silver}");
+    println!("gold: {gold}");
+
+    return Ok(());
+}
+
+fn trailheads(start: (usize, usize), grid: &Vec<Vec<u8>>, count_paths: bool) -> usize {
+    let mut seen = HashSet::new();
+    let mut tot = 0;
+    let mut q = vec![start];
+
+    while let Some(curr @ (y, x)) = q.pop() {
+        seen.insert(curr);
+        let h = grid[y][x];
+        if h == 9 {
+            tot += 1;
+            continue;
+        }
+
+        [
+            ((y + 1).min(grid.len() - 1), x),
+            (y, (x + 1).min(grid[0].len() - 1)),
+            (y.saturating_sub(1), x),
+            (y, x.saturating_sub(1)),
+        ]
+        .iter()
+        .filter(|&&(ny, nx)| grid[ny][nx] == h + 1)
+        .filter(|next| count_paths || !seen.contains(next))
+        .for_each(|&n| q.push(n));
+    }
+    tot
+}