Day 7

src/day7.rs

@@ -0,0 +1,188 @@
+static INPUT: &str = include_str!("inputs/day7.txt");
+
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+struct FileID(usize);
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+struct DirID(usize);
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+enum DirEntryKind {
+	File(FileID),
+	Dir(DirID),
+}
+#[derive(Debug)]
+struct DirEntry {
+	name: String,
+	kind: DirEntryKind,
+}
+
+#[derive(Debug)]
+struct File {
+	size: usize,
+}
+#[derive(Debug)]
+struct Dir {
+	parent: DirID,
+	children: Vec<DirEntry>,
+}
+
+#[derive(Debug)]
+struct Fs {
+	files: Vec<File>,
+	dirs: Vec<Dir>,
+}
+impl Fs {
+	fn new() -> Self {
+		Self {
+			files: vec![],
+			dirs: vec![Dir {
+				parent: DirID(0),
+				children: vec![],
+			}],
+		}
+	}
+
+	fn root(&self) -> DirID {
+		DirID(0)
+	}
+
+	fn mkdir(&mut self, target: DirID, name: &str) -> DirID {
+		let new_id = DirID(self.dirs.len());
+		self.dirs.push(Dir {
+			parent: target,
+			children: vec![],
+		});
+		self.dirs[target.0].children.push(DirEntry {
+			name: name.to_string(),
+			kind: DirEntryKind::Dir(new_id),
+		});
+
+		new_id
+	}
+
+	fn mkfile(&mut self, target: DirID, name: &str, size: usize) -> FileID {
+		let new_id = FileID(self.files.len());
+		self.files.push(File { size });
+		self.dirs[target.0].children.push(DirEntry {
+			name: name.to_string(),
+			kind: DirEntryKind::File(new_id),
+		});
+
+		new_id
+	}
+
+	fn entry(&self, target: DirID, name: &str) -> DirEntryKind {
+		let dir = &self.dirs[target.0];
+
+		dir.children
+			.iter()
+			.find(|e| e.name == name)
+			.map(|e| e.kind)
+			.unwrap()
+	}
+
+	fn parent(&self, target: DirID) -> DirID {
+		self.dirs[target.0].parent
+	}
+
+	fn dirsz(&self, target: DirID) -> usize {
+		let dir = &self.dirs[target.0];
+
+		dir.children
+			.iter()
+			.map(|c| match c.kind {
+				DirEntryKind::File(fid) => self.files[fid.0].size,
+				DirEntryKind::Dir(did) => self.dirsz(did),
+			})
+			.sum()
+	}
+}
+
+fn make_fs(s: &str) -> Fs {
+	let mut lines = s.split('\n').filter(|s| !s.is_empty()).peekable();
+
+	let mut fs = Fs::new();
+	let mut current_dir = fs.root();
+
+	while let Some(line) = lines.next() {
+		assert!(line.starts_with('$'));
+		let mut parts = line.split(' ').skip(1);
+
+		match parts.next().unwrap() {
+			"cd" => {
+				let arg = parts.next().unwrap();
+
+				current_dir = match arg {
+					"/" => fs.root(),
+					".." => fs.parent(current_dir),
+					_ => {
+						let entry = fs.entry(current_dir, arg);
+						match entry {
+							DirEntryKind::Dir(d) => d,
+							_ => panic!(),
+						}
+					}
+				};
+			}
+			"ls" => {
+				while let Some(data_line) = lines.peek() {
+					if data_line.starts_with('$') {
+						break;
+					}
+
+					let mut parts = data_line.split(' ');
+					let ty = parts.next().unwrap();
+					let name = parts.next().unwrap();
+
+					match ty {
+						"dir" => {
+							fs.mkdir(current_dir, name);
+						}
+						_ => {
+							let sz: usize = ty.parse().unwrap();
+							fs.mkfile(current_dir, name, sz);
+						}
+					}
+
+					lines.next();
+				}
+			}
+			_ => panic!(),
+		}
+	}
+
+	fs
+}
+
+pub fn part1() {
+	let fs = make_fs(INPUT);
+
+	println!(
+		"{}",
+		fs.dirs
+			.iter()
+			.enumerate()
+			.map(|(did, _)| fs.dirsz(DirID(did)))
+			.filter(|sz| sz <= &100000)
+			.sum::<usize>()
+	);
+}
+
+pub fn part2() {
+	let fs = make_fs(INPUT);
+	let total = 70_000_000;
+	let needed_free = 30_000_000;
+	let used = fs.dirsz(fs.root());
+	let free = total - used;
+	let diff = needed_free - free;
+
+	println!(
+		"{}",
+		fs.dirs
+			.iter()
+			.enumerate()
+			.map(|(did, _)| fs.dirsz(DirID(did)))
+			.filter(|sz| sz >= &diff)
+			.min()
+			.unwrap()
+	);
+}

src/main.rs

@@ -6,8 +6,9 @@ mod day3;
 mod day4;
 mod day5;
 mod day6;
+mod day7;
 mod util;
 
 fn main() {
-	day6::part2();
+	day7::part2();
 }