diff --git a/year2024/src/day25.rs b/year2024/src/day25.rs
new file mode 100644
index 0000000..38a5332
--- /dev/null
+++ b/year2024/src/day25.rs
@@ -0,0 +1,122 @@
+use common::day::Day;
+use util::grid2d::{Coords, Grid2D};
+
+pub struct Day25 {}
+
+impl Day for Day25 {
+    fn star1(&self, input: &str) -> String {
+        let (locks, keys) = parse_input(input);
+        pairs(&locks, &keys).to_string()
+    }
+
+    fn star2(&self, _input: &str) -> String {
+        String::from("not implemented")
+    }
+}
+
+type PinHeights = Vec<i64>;
+
+fn parse_input(input: &str) -> (Vec<PinHeights>, Vec<PinHeights>) {
+    let mut locks = vec![];
+    let mut keys = vec![];
+
+    for sec in input.split("\n\n") {
+        let grid = Grid2D::new(sec).unwrap();
+        let is_lock = grid.at(&Coords { x: 0, y: 0 }).unwrap() == &'#';
+
+        if is_lock {
+            locks.push(pin_heights(&grid, is_lock));
+        } else {
+            keys.push(pin_heights(&grid, is_lock));
+        }
+    }
+
+    (locks, keys)
+}
+
+fn pin_heights(grid: &Grid2D<char>, is_lock: bool) -> PinHeights {
+    let mut heights = vec![];
+
+    for x in 0..grid.width() {
+        let mut h = 0;
+        if is_lock {
+            while h < 5 && grid.at(&Coords { x, y: 1 + h }).unwrap() == &'#' {
+                h += 1;
+            }
+        } else {
+            while h < 5 && grid.at(&Coords { x, y: 5 - h }).unwrap() == &'#' {
+                h += 1;
+            }
+        }
+        heights.push(h);
+    }
+
+    heights
+}
+
+fn fits(lock: &PinHeights, key: &PinHeights) -> bool {
+    lock.iter().zip(key.iter()).all(|(l, k)| l + k <= 5)
+}
+
+fn pairs(locks: &[PinHeights], keys: &[PinHeights]) -> usize {
+    let mut count = 0;
+    for lock in locks {
+        for key in keys {
+            if fits(lock, key) {
+                count += 1;
+            }
+        }
+    }
+    count
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = r#"#####
+.####
+.####
+.####
+.#.#.
+.#...
+.....
+
+#####
+##.##
+.#.##
+...##
+...#.
+...#.
+.....
+
+.....
+#....
+#....
+#...#
+#.#.#
+#.###
+#####
+
+.....
+.....
+#.#..
+###..
+###.#
+###.#
+#####
+
+.....
+.....
+.....
+#....
+#.#..
+#.#.#
+#####"#;
+
+    #[test]
+    fn ex1() {
+        let d = Day25 {};
+        assert_eq!(d.star1(INPUT), "3");
+    }
+}
diff --git a/year2024/src/lib.rs b/year2024/src/lib.rs
index 4f1993c..f800428 100644
--- a/year2024/src/lib.rs
+++ b/year2024/src/lib.rs
@@ -25,6 +25,7 @@ mod day21;
 mod day22;
 mod day23;
 mod day24;
+mod day25;
 
 pub struct Year2024 {}
 
@@ -55,6 +56,7 @@ impl Year for Year2024 {
             22 => Some(Box::new(day22::Day22 {})),
             23 => Some(Box::new(day23::Day23 {})),
             24 => Some(Box::new(day24::Day24 {})),
+            25 => Some(Box::new(day25::Day25 {})),
             _ => None,
         }
     }