diff --git a/d7/Cargo.lock b/d7/Cargo.lock
new file mode 100644
index 0000000..30cae7a
--- /dev/null
+++ b/d7/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "d7"
+version = "0.1.0"
diff --git a/d7/Cargo.toml b/d7/Cargo.toml
new file mode 100644
index 0000000..22b9faf
--- /dev/null
+++ b/d7/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "d7"
+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/d7/src/main.rs b/d7/src/main.rs
new file mode 100644
index 0000000..53696bc
--- /dev/null
+++ b/d7/src/main.rs
@@ -0,0 +1,127 @@
+use std::{cell::RefCell, collections::HashMap, fs::read_to_string, io::Result, rc::Rc};
+
+#[derive(Debug)]
+enum Entry {
+    Dir(Option<RME>, HashMap<String, RME>),
+    File(usize),
+}
+
+type RME = Rc<RefCell<Entry>>;
+
+impl Entry {
+    pub fn new_dir<S: AsRef<str>>(parent: &Option<RME>, name: S) -> RME {
+        let this = Rc::new(RefCell::new(Entry::Dir(parent.clone(), HashMap::new())));
+        let this_clone = this.clone();
+        match parent {
+            Some(parent) => match &mut *parent.borrow_mut() {
+                Entry::Dir(_, ref mut children) => {
+                    children.insert(name.as_ref().to_owned(), this_clone);
+                }
+                _ => panic!("Attaching a child to a file"),
+            },
+            None => (),
+        }
+
+        this
+    }
+
+    pub fn new_file<S: AsRef<str>>(parent: RME, name: S, size: usize) -> RME {
+        let this = Rc::new(RefCell::new(Entry::File(size)));
+        let this_clone = this.clone();
+        match &mut *parent.borrow_mut() {
+            Entry::Dir(_, ref mut children) => {
+                children.insert(name.as_ref().to_owned(), this_clone);
+            }
+            _ => panic!("Attaching a child to a file"),
+        }
+        this
+    }
+
+    pub fn size(&self) -> usize {
+        match self {
+            Entry::File(size) => *size,
+            Entry::Dir(_, ref children) => children.values().map(|f| f.borrow().size()).sum(),
+        }
+    }
+
+    pub fn parent(&self) -> RME {
+        match self {
+            Entry::Dir(parent, _) => parent.as_ref().unwrap().clone(),
+            _ => panic!("Get parent for file"),
+        }
+    }
+
+    pub fn file<S: AsRef<str>>(&self, name: S) -> RME {
+        match self {
+            Entry::Dir(_, ref children) => children.get(name.as_ref()).unwrap().clone(),
+            _ => panic!("Get file for file"),
+        }
+    }
+
+    pub fn iter_dirs<F: FnMut(&Self)>(&self, f: &mut F) {
+        match self {
+            Entry::Dir(_, ref children) => {
+                f(self);
+                for child in children.values() {
+                    child.borrow().iter_dirs(f);
+                }
+            }
+            _ => (),
+        }
+    }
+}
+
+fn main() -> Result<()> {
+    let none = None;
+    let root = Entry::new_dir(&none, "/");
+
+    let mut current = root.clone();
+
+    for line in read_to_string("input.txt")?
+        .split("\n")
+        .filter(|x| !x.is_empty())
+    {
+        if line.starts_with("$ cd ") {
+            let path = line.split_at(5).1;
+
+            if path == "/" {
+                current = root.clone();
+            } else if path == ".." {
+                let next = current.borrow().parent();
+                current = next;
+            } else {
+                let next = current.borrow().file(path);
+                current = next;
+            }
+        } else if line == "$ ls" {
+            // ignore
+        } else if line.starts_with("dir ") {
+            let path = line.split_at(4).1;
+            Entry::new_dir(&Some(current.clone()), path);
+        } else {
+            let split = line.split(" ").collect::<Vec<_>>();
+            let size = split[0].parse::<usize>().unwrap();
+            let path = split[1];
+            Entry::new_file(current.clone(), path, size);
+        }
+    }
+
+    let mut sum_p1 = 0;
+    let mut smallest_p2 = usize::MAX;
+
+    let to_free = 30000000usize - (70000000usize - root.borrow().size());
+    root.borrow().iter_dirs(&mut |dir| {
+        let size = dir.size();
+        if size <= 100000 {
+            sum_p1 += size
+        }
+        if size >= to_free && size <= smallest_p2 {
+            smallest_p2 = size
+        }
+    });
+
+    println!("Part 1: {}", sum_p1);
+    println!("Part 2: {}", smallest_p2);
+
+    Ok(())
+}