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use {
anyhow::{
anyhow,
Context,
Result,
},
regex::Regex,
std::{
collections::HashMap,
env::args,
fs::File,
io::{
BufRead,
BufReader,
},
path::Path,
},
};
#[derive(Debug,PartialEq)]
struct FileDetails {
size: usize,
}
#[derive(Debug,PartialEq)]
struct FileTree {
tree: HashMap<String, EntryNode>,
}
#[derive(Debug,PartialEq)]
enum EntryNode {
File(FileDetails),
Directory(FileTree),
}
impl FileTree {
fn default() -> Self {
Self {
tree: HashMap::new(),
}
}
fn chdir(&mut self, path: &[String]) -> Option<&mut Self> {
if let Some((i, directory)) = path.iter().enumerate().find(|(_, name)| *name != "/") {
if let Some(node) = self.tree.get_mut(directory) {
match node {
EntryNode::File(_) => panic!("Tried to chdir into a file."),
EntryNode::Directory(tree) => tree.chdir(&path[(i + 1)..]),
}
} else {
None
}
} else {
Some(self)
}
}
fn size(&self) -> usize {
let mut size = 0;
for node in self.tree.values() {
match node {
EntryNode::File(file) => size += file.size,
EntryNode::Directory(directory) => size += directory.size(),
}
}
size
}
fn traverse(&self) -> TreeTraverse {
TreeTraverse::new(self)
}
}
struct TreeTraverse<'a> {
tree: &'a FileTree,
visited: Vec<&'a EntryNode>,
}
impl<'a> TreeTraverse<'a> {
fn new(tree: &'a FileTree) -> Self {
Self {
tree,
visited: vec![],
}
}
fn recurse(&mut self, tree: &'a FileTree) -> Option<&'a EntryNode> {
for node in tree.tree.values() {
if self.visited.contains(&node) {
continue;
}
match node {
EntryNode::File(_) => {
self.visited.push(node);
return Some(node);
},
EntryNode::Directory(subdir) => {
return self.recurse(subdir).or_else(|| {
self.visited.push(node);
Some(node)
});
}
}
}
None
}
}
impl<'a> Iterator for TreeTraverse<'a> {
type Item = &'a EntryNode;
fn next(&mut self) -> Option<&'a EntryNode> {
self.recurse(self.tree)
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<FileTree> {
let reader = BufReader::new(File::open(filename)?);
let re = Regex::new(r#"(?x)^
(\$\s+(?P<command>\S+)(\s+(?P<arg>\S+))?)|
(dir\s+(?P<directory>.+))|
((?P<size>[0-9]+)\s+(?P<filename>\S+))
$"#).context("Could not compile regex.")?;
let mut root = FileTree::default();
let mut path = vec![];
for (lineno, v) in reader.lines().enumerate() {
let node = root.chdir(&path).ok_or_else(|| anyhow!("Path {path:?} does not exist"))?;
let s = v?;
let caps = re.captures(&s)
.ok_or_else(|| anyhow!("Regex matching failed on line {lineno}: '{s}'"))?;
if let Some(command) = caps.name("command") {
match command.as_str() {
"cd" => {
if let Some(arg) = caps.name("arg") {
let dir = arg.as_str();
if dir == ".." {
path.pop();
} else if dir == "." {
// Remain in current directory.
} else {
path.push(String::from(dir));
}
}
},
"ls" => { },
cmd => return Err(anyhow!("Unknown command: '{cmd}'.")),
}
} else if let Some(dir_cap) = caps.name("directory") {
let directory = dir_cap.as_str();
node.tree.insert(String::from(directory), EntryNode::Directory(FileTree::default()));
} else if let (Some(cap_f), Some(cap_s)) = (caps.name("filename"), caps.name("size")) {
let str_s = cap_s.as_str();
let size = str_s.parse().context("Parse error: {str_s}")?;
let filename = cap_f.as_str();
node.tree.insert(String::from(filename), EntryNode::File(FileDetails { size }));
} else {
unreachable!();
}
}
Ok(root)
}
fn part1(input: &FileTree) -> Result<usize> {
Ok(input.traverse().filter_map(|node|
if let EntryNode::Directory(directory) = node {
let size = directory.size();
if size <= 100000 {
Some(size)
} else {
None
}
} else {
None
}).sum())
}
fn part2(input: &FileTree) -> Result<usize> {
let capacity = 70000000;
let required = 30000000;
let used = input.size();
let reclaim = required + used - capacity;
input.traverse().filter_map(|node|
if let EntryNode::Directory(directory) = node {
let size = directory.size();
if size >= reclaim {
Some(size)
} else {
None
}
} else {
None
}).min().ok_or_else(|| anyhow!("No suitable directory found"))
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
let input = read_input(filename).context("Could not read input")?;
if do_part_1 {
let solution = part1(&input).context("No solution for part 1")?;
println!("Part1, solution found to be: {}", solution);
}
if do_part_2 {
let solution = part2(&input).context("No solution for part 2")?;
println!("Part2, solution found to be: {}", solution);
}
Ok(())
}
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