diff --git a/src/day10.rs b/src/day10.rs
new file mode 100644
index 0000000..58358aa
--- /dev/null
+++ b/src/day10.rs
@@ -0,0 +1,53 @@
+use std::collections::VecDeque;
+use aoc_runner_derive::{aoc, aoc_generator};
+#[aoc_generator(day10)]
+fn parse(input: &str) -> Vec<char> {
+    input.chars().collect()
+}
+
+#[aoc(day10, part1)]
+fn part1(input: &Vec<char>) -> usize {
+    solve(input, 40).len()
+}
+
+fn solve(input: &Vec<char>, runs: usize) -> String {
+    let mut saying: VecDeque<char> = input.iter().map(|c| *c).collect();
+    let mut next: VecDeque<char> = VecDeque::new();
+    for _ in 0..runs {
+        while let Some(current) = saying.pop_front() {
+            let mut count = 1;
+            while saying.front() == Some(&current) {
+                count += 1;
+                saying.pop_front();
+            }
+            let s = format!("{count}{current}");
+            for c in s.chars() {
+                next.push_back(c);
+            }
+        }
+        saying = next;
+        next = VecDeque::new();
+    }
+    saying.into_iter().collect()
+}
+
+#[aoc(day10, part2)]
+fn part2(input: &[char]) -> String {
+    todo!()
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(solve(&parse("111221"), 1), "312211");
+    }
+
+    // #[test]
+    // fn part2_example() {
+    //     assert_eq!(part2(&parse("<EXAMPLE>")), "<RESULT>");
+    // }
+}
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 11f70a2..a434274 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,7 @@
 extern crate aoc_runner;
-
 #[macro_use]
 extern crate aoc_runner_derive;
 
-aoc_lib!{ year = 2015 }
+mod day10;
+
+aoc_lib! { year = 2015 }