And there's part 2

2022/src/day7.rs

@@ -6,7 +6,7 @@ use nom::{
     },
     combinator::eof,
     multi::many0,
-    sequence::{self, terminated},
+    sequence::terminated,
     IResult, Parser,
 };
 use std::{
@@ -21,7 +21,7 @@ pub fn part1() -> String {
 }
 
 pub fn part2() -> String {
-    unimplemented!()
+    format!("{}", find_minimum_directory(&input(INPUT)).1)
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -66,6 +66,18 @@ fn tree_sizes_100k(filesystem: &Filesystem) -> usize {
         .fold(0, |cur, size| cur + size)
 }
 
+fn find_minimum_directory(filesystem: &Filesystem) -> (PathBuf, usize) {
+    let needed_space = 30000000 - filesystem.free_space();
+    let mut dir_sizes = filesystem
+        .find_dirs()
+        .iter()
+        .map(|path| (path.clone(), filesystem.size(path)))
+        .filter(|(_, size)| needed_space < (*size).try_into().unwrap())
+        .collect::<Vec<(PathBuf, usize)>>();
+    dir_sizes.sort_by(|(_, lsize), (_, rsize)| lsize.cmp(rsize));
+    dir_sizes[0].clone()
+}
+
 #[derive(Clone, Debug, PartialEq)]
 enum Command {
     CD(String),
@@ -113,6 +125,10 @@ impl Filesystem {
             .cloned()
             .collect()
     }
+
+    fn free_space(&self) -> usize {
+        70000000 - self.size(&PathBuf::from("/"))
+    }
 }
 
 impl Default for Filesystem {
@@ -145,10 +161,6 @@ impl Default for State {
 }
 
 impl State {
-    fn paths(&self) -> HashSet<PathBuf> {
-        self.filesystem.paths()
-    }
-
     fn interpret_line(&mut self, line: SessionLine) {
         match line {
             SessionLine::Output(entry) => self.add_entry(entry),
@@ -513,4 +525,19 @@ $ ls
     fn it_solves_part1() {
         assert_eq!(tree_sizes_100k(&input(INPUT)), 1792222);
     }
+
+    #[test]
+    fn it_measures_free_space() {
+        with_input(|fs| assert_eq!(fs.free_space(), 21618835));
+    }
+
+    #[test]
+    fn it_finds_smallest_needed_dir() {
+        with_input(|fs| assert_eq!(find_minimum_directory(&fs), (PathBuf::from("/d"), 24933642)));
+    }
+
+    #[test]
+    fn it_solves_part2() {
+        assert_eq!(find_minimum_directory(&input(INPUT)).1, 1112963);
+    }
 }