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use anyhow::{anyhow, Result};
use std::env::args;
use std::fs::File;
use std::io::{BufRead, BufReader};
use std::ops::RangeInclusive;
use std::path::Path;
use thiserror::Error;
#[derive(Error, Debug)]
enum BinarySpaceError {
#[error("Space is not fully reduced")]
NotReduced,
}
struct BinarySpace {
start: usize,
end: usize,
}
impl BinarySpace {
fn new(range: RangeInclusive<usize>) -> BinarySpace
// FIXME It would be nice with a cleaner interface. The intention was to use something like the
// RangeBounds trait, but it seems to require support of Unbounded ranges, which this
// BinarySpace will not be able to work with.
{
BinarySpace {
start: *range.start(),
end: *range.end(),
}
}
fn size(&self) -> usize {
self.end - self.start
}
fn split(&mut self, op: char) {
let size = self.size() + 1;
let half = size / 2;
match op {
'F' | 'L' => self.end -= half,
'B' | 'R' => self.start += half,
c => panic!("Invalid op to BinarySpace.split(): {}", c),
}
}
fn value(&self) -> std::result::Result<usize, BinarySpaceError> {
if self.start == self.end {
Ok(self.start)
} else {
Err(BinarySpaceError::NotReduced)
}
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> std::io::Result<Vec<String>> {
let f = File::open(filename)?;
let reader = BufReader::new(f);
reader.lines().collect()
}
fn parse_boarding_passes(input: &[String]) -> Result<Vec<usize>> {
input.iter().map(|ops| {
let mut row = BinarySpace::new(0..=127);
let mut col = BinarySpace::new(0..=7);
for op in ops.clone().drain(..) {
match op {
'F' | 'B' => row.split(op),
'L' | 'R' => col.split(op),
_ => return Err(anyhow!("Invalid op encountered")),
}
}
Ok(row.value()? * 8 + col.value()?)
}).collect()
}
fn part1(input: &[usize]) -> Option<usize> {
input.iter().max().copied()
}
fn part2(input: &[usize]) -> Option<usize> {
let mut ret = None;
for seat in 1..(128*8) {
if (input.contains(&seat),
input.contains(&(seat-1)),
input.contains(&(seat+1))
) == (false, true, true) {
match ret {
None => ret = Some(seat),
Some(_) => return None, /* No more than one solution allowed */
}
}
}
ret
}
fn main() {
let (do_part_1, do_part_2) = aoc::do_parts();
let filename = match args().nth(1) {
Some(f) => f,
None => {
eprintln!("Missing input filename");
std::process::exit(1);
},
};
match read_input(filename) {
Ok(input) => {
match parse_boarding_passes(&input) {
Ok(seat_ids) => {
if do_part_1 {
match part1(&seat_ids) {
Some(solution) =>
println!("Part1, highest seat ID found to be: {}", solution),
None => eprintln!("Part1, no soluton found"),
}
}
if do_part_2 {
match part2(&seat_ids) {
Some(solution) =>
println!("Part2, seat {} is lacking a boarding pass", solution),
None => eprintln!("Part2, no soluton found"),
}
}
},
Err(err) => eprintln!("Could not parse input: {}", err),
}
},
Err(err) => eprintln!("Could not read input: {}", err),
}
}
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