Day 7 part 1

2022/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "advent-of-code"
+version = "0.1.0"

2022/Cargo.toml

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+[package]
+name = "advent-of-code"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2022/src/bin/day7.rs

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+use std::cell::RefCell;
+use std::io::{self};
+use std::ops::DerefMut;
+use std::rc::Rc;
+
+const LIMIT: usize = 100_000;
+
+type Node<'a> = Rc<RefCell<FsNode<'a>>>;
+
+struct FsNode<'a> {
+    parent: Option<Node<'a>>,
+    data: FsNodeData<'a>,
+}
+enum FsNodeData<'a> {
+    Dir(Dir<'a>),
+    File(File<'a>),
+}
+
+struct Dir<'a> {
+    name: &'a str,
+    size: usize,
+    children: Vec<Node<'a>>,
+}
+
+struct File<'a> {
+    name: &'a str,
+    size: usize,
+}
+
+fn main() -> io::Result<()> {
+    let input = std::fs::read_to_string("input/day_7.txt")?;
+    let root = new_node(None, FsNodeData::Dir(Dir::new("/")));
+    let mut pwd = Rc::clone(&root);
+
+    for line in input.lines() {
+        match line.chars().next() {
+            Some('$') => pwd = execute_cmd(&line[1..], Rc::clone(&pwd), &root)?,
+            Some('d') => add_dir(line, Rc::clone(&pwd))?,
+            Some(c) if c.is_ascii_digit() => add_file(line, Rc::clone(&pwd))?,
+            c => panic!("unexpected character: {:?}", c),
+        }
+    }
+
+    // Traverse the filesystem tree looking for large dirs
+    let sum_of_large_dirs = traverse(&root.borrow());
+    println!("{}", sum_of_large_dirs);
+
+    Ok(())
+}
+
+fn traverse(node: &FsNode<'_>) -> usize {
+    let mut sum = 0;
+    match &node.data {
+        FsNodeData::Dir(Dir { size, children, .. }) => {
+            if *size <= LIMIT {
+                sum += size
+            }
+            for child in children {
+                sum += traverse(&child.borrow())
+            }
+            sum
+        }
+        FsNodeData::File(_) => 0,
+    }
+}
+
+/// Execute a command, returning the new pwd
+fn execute_cmd<'a, 'b>(line: &'a str, pwd: Node<'b>, root: &'a Node<'b>) -> io::Result<Node<'b>> {
+    let mut words = line.trim().split(' ');
+    let cmd = words.next();
+    let arg = words.next();
+    match (cmd, arg) {
+        (Some("ls"), None) => Ok(pwd),
+        (Some("cd"), Some("..")) => pwd
+            .borrow()
+            .parent
+            .as_ref()
+            .map(Rc::clone)
+            .ok_or_else(|| err("node has no parent")),
+        (Some("cd"), Some("/")) => Ok(Rc::clone(root)),
+        (Some("cd"), Some(dir)) => {
+            let pwd = pwd.borrow();
+            let FsNode { data: FsNodeData::Dir(pwd), .. } = &*pwd else {
+                return Err(err("pwd is not a dir"))
+            };
+            pwd.children
+                .iter()
+                .find(|child| {
+                    matches!(
+                        *child.borrow(),
+                        FsNode {
+                            data: FsNodeData::Dir(Dir { name, .. }),
+                            ..
+                        } if name == dir
+                    )
+                })
+                .ok_or_else(|| err("node has no parent"))
+                .cloned()
+        }
+        _ => Err(err("unexpected command")),
+    }
+}
+
+fn add_dir<'a>(line: &'a str, pwd: Node<'a>) -> io::Result<()> {
+    let mut words = line.trim().split(' ');
+    let Some("dir") = words.next() else {
+        return Err(err("didn't get dir"))
+    };
+    let Some(name) = words.next() else {
+        return Err(err("missing dir name"))
+    };
+
+    let mut dir = pwd.borrow_mut();
+    let FsNode { data: FsNodeData::Dir(dir), .. } = dir.deref_mut() else {
+        return Err(err("pwd is not a dir"))
+    };
+    dir.children.push(new_node(
+        Some(Rc::clone(&pwd)),
+        FsNodeData::Dir(Dir::new(name)),
+    ));
+    Ok(())
+}
+
+fn add_file<'a>(line: &'a str, pwd: Node<'a>) -> io::Result<()> {
+    let mut words = line.trim().split(' ');
+    let size = words
+        .next()
+        .and_then(|size| size.parse::<usize>().ok())
+        .ok_or_else(|| err("file missing size"))?;
+    let Some(name) = words.next() else {
+        return Err(err("missing file name"))
+    };
+
+    let mut dir = pwd.borrow_mut();
+    let FsNode { data: FsNodeData::Dir(dir), parent, .. } = dir.deref_mut() else {
+        return Err(err("pwd is not a dir"))
+    };
+    dir.children.push(new_node(
+        Some(Rc::clone(&pwd)),
+        FsNodeData::File(File::new(name, size)),
+    ));
+    dir.size += size;
+    if let Some(parent) = parent {
+        update_size(size, &mut parent.borrow_mut());
+    }
+    Ok(())
+}
+
+fn update_size(size: usize, node: &mut FsNode<'_>) {
+    let FsNode { data: FsNodeData::Dir(dir), parent, .. } = node else {
+        panic!("node is not a dir")
+    };
+    dir.size += size;
+    if let Some(parent) = parent {
+        update_size(size, &mut parent.borrow_mut())
+    }
+}
+
+fn new_node<'a>(parent: Option<Node<'a>>, data: FsNodeData<'a>) -> Node<'a> {
+    Rc::new(RefCell::new(FsNode::new(parent, data)))
+}
+
+fn err(msg: &str) -> io::Error {
+    io::Error::new(io::ErrorKind::Other, msg)
+}
+
+impl<'a> FsNode<'a> {
+    fn new(parent: Option<Node<'a>>, data: FsNodeData<'a>) -> Self {
+        FsNode { parent, data }
+    }
+}
+
+impl<'a> Dir<'a> {
+    fn new(name: &'a str) -> Self {
+        Dir {
+            size: 0,
+            name,
+            children: Vec::new(),
+        }
+    }
+}
+
+impl<'a> File<'a> {
+    fn new(name: &'a str, size: usize) -> Self {
+        File { name, size }
+    }
+}