diff --git a/day07/Cargo.lock b/day07/Cargo.lock
new file mode 100644
index 0000000..cf14c74
--- /dev/null
+++ b/day07/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day07"
+version = "0.1.0"
diff --git a/day07/Cargo.toml b/day07/Cargo.toml
new file mode 100644
index 0000000..682e4ad
--- /dev/null
+++ b/day07/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day07"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day07/src/main.rs b/day07/src/main.rs
new file mode 100644
index 0000000..ad37050
--- /dev/null
+++ b/day07/src/main.rs
@@ -0,0 +1,160 @@
+use std::cell::RefCell;
+use std::error;
+use std::fs::File;
+use std::io::BufRead;
+use std::io::BufReader;
+use std::rc::{Rc, Weak};
+
+
+enum FsEntry {
+	Dir(Rc<FsDir>),
+	File(FsFile)
+}
+
+struct FsDir {
+	name: String,
+	children: RefCell<Vec<FsEntry>>,
+	parent: Option<Weak<FsDir>>
+}
+
+impl FsDir {
+	fn _compute_size(&self) -> u32 {
+		let mut size: u32 = 0;
+		let children = self.children.borrow_mut();
+		for child in children.iter() {
+			match child {
+				FsEntry::File(f) => size += f.size,
+				FsEntry::Dir(d) => {
+					size += d._compute_size();
+				},
+			};
+		}
+		size
+	}
+
+	fn _show(&self, prefix: String) {
+		println!("{}{}", &prefix, &self.name);
+		let children = self.children.borrow_mut();
+		for child in children.iter() {
+			match child {
+				FsEntry::File(f) => println!("{}{}", &prefix, &f.size),
+				FsEntry::Dir(d) => d._show(format!("{}  ", &prefix)),
+			};
+		}
+	}
+
+	fn get_dir_sizes(&self) -> Vec<u32> {
+		let mut sizes = vec![];
+		let mut size: u32 = 0;
+		let children = self.children.borrow_mut();
+		for child in children.iter() {
+			match child {
+				FsEntry::File(f) => size += f.size,
+				FsEntry::Dir(d) => {
+					let d_vec = d.get_dir_sizes();
+					size += d_vec[d_vec.len() - 1];
+					sizes.extend_from_slice(&d_vec);
+				},
+			};
+		}
+		sizes.push(size);
+		sizes
+	}
+}
+
+struct FsFile {
+	size: u32
+}
+
+fn main() -> Result<(), Box<dyn error::Error>> {
+	let f = File::open("input.txt")?;
+	let reader = BufReader::new(f);
+
+	let fs_tree: Rc<FsDir> = Rc::new(FsDir { children: RefCell::new(vec![]), parent: None, name: String::from("/") });
+	let mut current_dir = Rc::downgrade(&fs_tree);
+
+	for line in reader.lines() {
+		let line = line?;
+		if &line[0..1] == "$" {
+			// parse the command
+			let mut cmd_iter = line[2..].split_whitespace();
+			match cmd_iter.next() {
+				Some("cd") => {
+					// println!("{}", &line);
+					match cmd_iter.next() {
+						Some("/") => current_dir = Rc::downgrade(&fs_tree),
+						Some("..") => {
+							let mut new_dir = None;
+							let strong = current_dir.upgrade().unwrap();
+							match &strong.parent {
+								Some(x) => {
+									let strong_x = x.upgrade().unwrap();
+									let rc_c = Rc::clone(&strong_x);
+									new_dir = Some(Rc::downgrade(&rc_c));
+								},
+								None => (),
+							};
+							match new_dir {
+								Some(d) => current_dir = d,
+								None => panic!("Could not find parent dir in '{}'", current_dir.upgrade().unwrap().name),
+							};
+						},
+						Some(x) => {
+							let mut new_dir = None;
+							let strong = current_dir.upgrade().unwrap();
+							let children = strong.children.borrow_mut();
+							for child in children.iter() {
+								if let FsEntry::Dir(d) = child {
+									if d.name == x {
+										new_dir = Some(Rc::clone(&d));
+										break;
+									}
+								}
+							}
+							match new_dir {
+								Some(d) => current_dir = Rc::downgrade(&d),
+								None => panic!("Could not find dir '{x}' in '{}'", current_dir.upgrade().unwrap().name),
+							}
+						},
+						None => panic!("No argument to 'cd': {}", line),
+					};
+					// println!("{}", current_dir.upgrade().unwrap().name);
+				},
+				Some("ls") => {
+					// we can ignore this, as we read everything not being a command into the
+					// current directory anyways
+				}
+				Some(x) => panic!("Unsupported command: {}", x),
+				None => panic!("Could not split into a command: {}", line),
+			};
+		} else {
+			// parse the list of fs entries
+			let mut entry_iter = line.split_whitespace();
+			match entry_iter.next() {
+				Some("dir") => {
+					let new_dir = Rc::new(FsDir {name: String::from(entry_iter.next().unwrap()),
+										         children: RefCell::new(vec![]), parent: Some(current_dir.clone()) });
+					let strong = current_dir.upgrade().unwrap();
+					let mut children = strong.children.borrow_mut();
+					children.push(FsEntry::Dir(new_dir));
+				},
+				Some(size) => {
+					let f = FsFile {size: size.parse().unwrap()};
+					let strong = current_dir.upgrade().unwrap();
+					let mut children = strong.children.borrow_mut();
+					children.push(FsEntry::File(f));
+				},
+				_ => panic!("Unknown fs entry: {line}"),
+			};
+		}
+	}
+	drop(current_dir);
+	// fs_tree.show(String::from(""));
+
+	// compute sizes
+	let sizes = fs_tree.get_dir_sizes();
+	println!("{}", sizes.iter().filter(|x| **x < 100000).sum::<u32>());
+
+    println!("Hello, world!");
+    Ok(())
+}