1 files changed, 110 insertions, 0 deletions
diff --git a/2022/src/day07.rs b/2022/src/day07.rs
new file mode 100644
index 0000000..88bb647
--- /dev/null
+++ b/2022/src/day07.rs
@@ -0,0 +1,110 @@
+mod utils;
+use utils::read_input;
+
+fn main() {
+    let input = read_input();
+
+    let mut unused = 0;
+    let mut sum_under_threshold = 0;
+
+    for size in DirectorySizes::new(&input) {
+        if size < 100_000 {
+            sum_under_threshold += size;
+        }
+        unused = 70_000_000 - size;
+    }
+
+    println!("Part 1: {}", sum_under_threshold);
+    let deficit = 30_000_000 - unused;
+    println!(
+        "Part 2: {}",
+        DirectorySizes::new(&input)
+            .filter(|x| *x > deficit)
+            .min()
+            .unwrap()
+    );
+}
+
+struct DirectorySizes<'a> {
+    lines: std::str::Lines<'a>,
+    directory_stack: [usize; 64],
+    stack_top: usize,
+}
+
+impl<'a> DirectorySizes<'a> {
+    fn new(input: &'a str) -> Self {
+        let mut lines = input.lines();
+        assert_eq!(lines.next(), Some("$ cd /"));
+
+        DirectorySizes {
+            lines,
+            directory_stack: [0; 64],
+            stack_top: 0,
+        }
+    }
+}
+
+impl Iterator for DirectorySizes<'_> {
+    type Item = usize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        for line in self.lines.by_ref() {
+            let line: Line = line.into();
+
+            match line {
+                Line::Cd(up) => {
+                    if up {
+                        self.directory_stack[self.stack_top - 1] +=
+                            self.directory_stack[self.stack_top];
+                        self.stack_top -= 1;
+                        return Some(self.directory_stack[self.stack_top + 1]);
+                    } else {
+                        self.stack_top += 1;
+                        self.directory_stack[self.stack_top] = 0;
+                    }
+                }
+                Line::FileSize(size) => {
+                    self.directory_stack[self.stack_top] += size;
+                }
+                Line::Ls => (),
+                Line::Dir => (),
+            };
+        }
+
+        if self.stack_top > 0 {
+            self.directory_stack[self.stack_top - 1] += self.directory_stack[self.stack_top];
+            self.stack_top -= 1;
+            Some(self.directory_stack[self.stack_top + 1])
+        } else if self.directory_stack[0] != 0 {
+            Some(std::mem::replace(&mut self.directory_stack[0], 0))
+        } else {
+            None
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Line {
+    /// True = .., False = other
+    Cd(bool),
+    Ls,
+    FileSize(usize),
+    Dir,
+}
+
+impl From<&str> for Line {
+    fn from(value: &str) -> Self {
+        if value.starts_with("$ cd ") {
+            let mut args = value.split("cd ");
+            args.next().unwrap();
+            Line::Cd(args.next().unwrap() == "..")
+        } else if value.starts_with("$ ls") {
+            Line::Ls
+        } else if value.starts_with("dir") {
+            Line::Dir
+        } else {
+            let num_index = value.chars().take_while(|chr| chr.is_numeric()).count();
+            Line::FileSize(value[..num_index].parse().unwrap())
+        }
+    }
+}