diff --git a/2023/all.sh b/2023/all.sh
index f2531fe..d8c0023 100755
--- a/2023/all.sh
+++ b/2023/all.sh
@@ -35,6 +35,10 @@ run() {
   echo "day8"
   ./day8/target/release/day8 1
   ./day8/target/release/day8 2
+
+  echo "day9"
+  ./day9/target/release/day9 1
+  ./day9/target/release/day9 2
 }
 
 time run
diff --git a/2023/day9/.gitignore b/2023/day9/.gitignore
new file mode 100644
index 0000000..b83d222
--- /dev/null
+++ b/2023/day9/.gitignore
@@ -0,0 +1 @@
+/target/
diff --git a/2023/day9/Cargo.lock b/2023/day9/Cargo.lock
new file mode 100644
index 0000000..a412849
--- /dev/null
+++ b/2023/day9/Cargo.lock
@@ -0,0 +1,16 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day9"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+]
+
+[[package]]
+name = "indoc"
+version = "2.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e186cfbae8084e513daff4240b4797e342f988cecda4fb6c939150f96315fd8"
diff --git a/2023/day9/Cargo.toml b/2023/day9/Cargo.toml
new file mode 100644
index 0000000..778615e
--- /dev/null
+++ b/2023/day9/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day9"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+indoc = "2.0.4"
diff --git a/2023/day9/src/main.rs b/2023/day9/src/main.rs
new file mode 100644
index 0000000..6479c44
--- /dev/null
+++ b/2023/day9/src/main.rs
@@ -0,0 +1,131 @@
+use std::num::ParseIntError;
+
+fn part1(input: &str) -> Result<usize, String> {
+    let mut sum = 0;
+    for line in input.lines() {
+        let mut map: Vec<Vec<isize>> = vec![];
+
+        map.push(
+            line.split_whitespace()
+                .map(str::parse::<isize>)
+                .collect::<Result<Vec<isize>, ParseIntError>>()
+                .unwrap(),
+        );
+
+        for i in 0.. {
+            let reduced = map[i]
+                .windows(2)
+                .map(|w| w[1] - w[0])
+                .collect::<Vec<isize>>();
+
+            let all_zero = reduced.iter().all(|e| *e == 0);
+
+            map.push(reduced);
+
+            if all_zero {
+                break;
+            }
+        }
+
+        let len = map.len();
+
+        map[len - 1].push(0);
+
+        for i in (0..map.len() - 1).rev() {
+            let j = map[i].len();
+            let left = map[i][j - 1];
+            let below = map[i + 1][j - 1];
+            map[i].push(left + below);
+        }
+
+        sum += map[0].last().unwrap();
+    }
+
+    Ok(sum as usize)
+}
+
+fn part2(input: &str) -> Result<usize, String> {
+    let mut sum = 0;
+    for line in input.lines() {
+        let mut map: Vec<Vec<isize>> = vec![];
+
+        map.push(
+            line.split_whitespace()
+                .map(str::parse::<isize>)
+                .collect::<Result<Vec<isize>, ParseIntError>>()
+                .unwrap(),
+        );
+
+        for i in 0.. {
+            let reduced = map[i]
+                .windows(2)
+                .map(|w| w[1] - w[0])
+                .collect::<Vec<isize>>();
+
+            let all_zero = reduced.iter().all(|e| *e == 0);
+
+            map.push(reduced);
+
+            if all_zero {
+                break;
+            }
+        }
+
+        let len = map.len();
+
+        map[len - 1].insert(0, 0);
+
+        for i in (0..map.len() - 1).rev() {
+            let right = map[i][0];
+            let below = map[i + 1][0];
+            map[i].insert(0, right - below);
+        }
+
+        sum += map[0].first().unwrap();
+    }
+
+    Ok(sum as usize)
+}
+
+fn main() -> Result<(), String> {
+    let input = include_str!("../input");
+
+    let args = std::env::args().skip(1).collect::<Vec<String>>();
+    let part = args[0].parse::<usize>().unwrap();
+
+    if part == 1 {
+        println!("Part 1 : {}", part1(input)?);
+    } else if part == 2 {
+        println!("Part 2 : {}", part2(input)?);
+    } else {
+        return Err("unknown part".into());
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn part_1_example_1() {
+        let input = indoc! {"
+            0 3 6 9 12 15
+            1 3 6 10 15 21
+            10 13 16 21 30 45
+        "};
+        assert_eq!(part1(input).unwrap(), 114);
+    }
+
+    #[test]
+    fn part_2_example_1() {
+        let input = indoc! {"
+            0 3 6 9 12 15
+            1 3 6 10 15 21
+            10 13 16 21 30 45
+        "};
+        assert_eq!(part2(input).unwrap(), 2);
+    }
+}