diff --git a/9/Cargo.lock b/9/Cargo.lock
new file mode 100644
index 0000000..46e4d66
--- /dev/null
+++ b/9/Cargo.lock
@@ -0,0 +1,25 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day9"
+version = "0.1.0"
+dependencies = [
+ "itertools",
+]
+
+[[package]]
+name = "either"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60b1af1c220855b6ceac025d3f6ecdd2b7c4894bfe9cd9bda4fbb4bc7c0d4cf0"
+
+[[package]]
+name = "itertools"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "413ee7dfc52ee1a4949ceeb7dbc8a33f2d6c088194d9f922fb8318faf1f01186"
+dependencies = [
+ "either",
+]
diff --git a/9/Cargo.toml b/9/Cargo.toml
new file mode 100644
index 0000000..02224b3
--- /dev/null
+++ b/9/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "day9"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+itertools = "0.13.0"
diff --git a/9/src/main.rs b/9/src/main.rs
new file mode 100644
index 0000000..fb52b9a
--- /dev/null
+++ b/9/src/main.rs
@@ -0,0 +1,203 @@
+use std::collections::LinkedList;
+use std::fmt::{Display, Write};
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines};
+use std::time::{Duration, Instant};
+
+use itertools::Itertools;
+
+// BOILERPLATE
+type InputIter = Lines<BufReader<File>>;
+
+pub fn get_input() -> InputIter {
+    let f = File::open("input").unwrap();
+    let br = BufReader::new(f);
+    br.lines()
+}
+
+fn duration_format(duration: Duration) -> String {
+    match duration.as_secs_f64() {
+        x if x > 1.0 => format!("{:.3}s", x),
+        x if x > 0.010 => format!("{:.3}ms", x * 1e3),
+        x => format!("{:.3}us", x * 1e6),
+    }
+}
+
+fn main() {
+    let input = get_input();
+    let start = Instant::now();
+    let ans1 = problem1(input);
+    let duration1 = start.elapsed();
+    println!("Problem 1 solution: {} [{}]", ans1, duration_format(duration1));
+
+    let input = get_input();
+    let start = Instant::now();
+    let ans2 = problem2(input);
+    let duration2 = start.elapsed();
+    println!("Problem 2 solution: {} [{}]", ans2, duration_format(duration2));
+    println!("Total duration: {}", duration_format(duration1 + duration2));
+}
+
+#[derive(Debug, Eq, PartialEq, Clone, Copy)]
+enum Unit {
+    File(usize),
+    Free,
+}
+
+struct DiskMap {
+    map: Vec<Unit>,
+}
+
+impl<T: BufRead> From<Lines<T>> for DiskMap {
+    fn from(mut input: Lines<T>) -> Self {
+        let line_s = input.next().unwrap().unwrap();
+        let line = line_s.as_bytes();
+        let mut file_id = 0;
+        let mut map = Vec::new();
+        for i in 0..line.len() {
+            if i % 2 == 0 {
+                // file
+                for _ in 0..line[i] - b'0' {
+                    map.push(Unit::File(file_id))
+                }
+                file_id += 1;
+            } else {
+                // free
+                for _ in 0..line[i] - b'0' {
+                    map.push(Unit::Free)
+                }
+            }
+        }
+        Self { map }
+    }
+}
+
+impl Display for DiskMap {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        for unit in &self.map {
+            match unit {
+                Unit::File(i) => f.write_char((b'0' + (*i % 10) as u8) as char)?,
+                Unit::Free => f.write_char('.')?,
+            }
+        }
+        Ok(())
+    }
+}
+
+impl DiskMap {
+    fn checksum(&self) -> u64 {
+        self.map
+            .iter()
+            .enumerate()
+            .map(|(i, u)| match u {
+                Unit::File(id) => i * id,
+                Unit::Free => 0,
+            })
+            .sum::<usize>() as u64
+    }
+}
+
+// PROBLEM 1 solution
+
+fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
+    let mut map = DiskMap::from(input);
+    println!("{}", map);
+    println!();
+    let mut i = map.map.len() - 1;
+    while i != 0 {
+        // find start index of 'file'
+        if map.map[i] == Unit::Free {
+            i -= 1;
+            continue;
+        };
+        let mut len = 1;
+        while i >= 1 && map.map[i] == map.map[i - 1] {
+            i -= 1;
+            len += 1;
+        }
+        let file_id = match map.map[i] {
+            Unit::File(id) => id,
+            _ => panic!(),
+        };
+        let frees = map
+            .map
+            .iter()
+            .enumerate()
+            .take(i + len)
+            .filter(|(_i, u)| **u == Unit::Free || **u == Unit::File(file_id))
+            .map(|(i, _u)| i)
+            .take(len)
+            .collect_vec();
+        if frees[0] == i && i > 0 {
+            i -= 1;
+            continue;
+        }
+        for j in 0..len {
+            map.map.swap(frees[j], i + j);
+        }
+        if i > 0 {
+            i -= 1;
+        }
+    }
+    println!("{}", map);
+    map.checksum()
+}
+
+// PROBLEM 2 solution
+fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
+    let mut map = DiskMap::from(input);
+    let mut i = map.map.len() - 1;
+    while i != 0 {
+        // find start index of 'file'
+        if map.map[i] == Unit::Free {
+            i -= 1;
+            continue;
+        };
+        let mut len = 1;
+        while i >= 1 && map.map[i] == map.map[i - 1] {
+            i -= 1;
+            len += 1;
+        }
+        let free_pos = map
+            .map
+            .windows(len)
+            .enumerate()
+            .find(|(i, u)| {
+                u.iter().all(|u| match u {
+                    Unit::Free => true,
+                    _ => false,
+                })
+            })
+            .map(|(i, _)| i);
+        if let Some(free_pos) = free_pos {
+            for j in 0..len {
+                map.map[free_pos + j] = map.map[i + j];
+                map.map[i + j] = Unit::Free;
+            }
+        }
+        if i > 0 {
+            i -= 1;
+        }
+    }
+    0
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+    use std::io::Cursor;
+
+    const EXAMPLE: &str = &"2333133121414131402";
+
+    #[test]
+    fn problem1_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem1(c.lines()), 1928);
+    }
+
+    #[test]
+    fn problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 0);
+    }
+}