diff --git a/src/days.rs b/src/days.rs
index 1e38d08..ec4feb9 100644
--- a/src/days.rs
+++ b/src/days.rs
@@ -12,7 +12,7 @@ pub mod d11;
 pub mod d12;
 pub mod d13;
 pub mod d14;
-// pub mod d15;
+pub mod d15;
 // pub mod d16;
 // pub mod d17;
 // pub mod d18;
diff --git a/src/days/d15.rs b/src/days/d15.rs
new file mode 100644
index 0000000..35bf1a2
--- /dev/null
+++ b/src/days/d15.rs
@@ -0,0 +1,58 @@
+use crate::prelude::*;
+
+pub type I = Vec<(usize, usize)>;
+pub type O = usize;
+
+fn _parse (data: &str) -> I {
+    data.lines()
+        .map(|e| e.trim().trim_matches('.')
+            .split_once(" has ")
+            .map(|(_, r)|
+                r.split_once(" positions; at time=0, it is at position ")
+                    .map(|(n, p)| (n.parse().unwrap(), p.parse().unwrap()))
+            )
+            .flatten()
+            .unwrap()
+        )
+        .collect()
+}
+
+fn _solve (data: &I) -> O {
+    let d = |time, (size, position)| (time + position) % size == 0;
+    (0..).into_iter().find(|t| data.iter().enumerate().all(|(i, &df)| d(t + i + 1, df))).unwrap()
+}
+
+fn _silver (data: I) -> O {
+    _solve(&data)
+}
+
+fn _gold (mut data: I) -> O {
+    data.push((11, 0));
+    _solve(&data)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        let data = inc!(15);
+        _parse(data)
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(data);
+
+        assert_eq!(ans, 122318)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(data);
+
+        assert_eq!(ans, 3208583)
+    }
+}