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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())
}
}
}
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