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use {
anyhow::{
anyhow,
Context,
Result,
},
std::{
cmp::Ordering,
env::args,
fs::File,
io::{
BufRead,
BufReader,
},
path::Path,
},
};
type DiagnosticValue = usize;
struct Diagnostics {
bits: usize,
values: Vec<DiagnosticValue>,
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<Diagnostics> {
let reader = BufReader::new(File::open(filename)?);
let mut bit_count = None;
let mut values = Vec::new();
for row in reader.lines() {
let string = row?;
if bit_count.is_none() {
bit_count = Some(string.len());
}
let value = usize::from_str_radix(&string, 2)
.map_err(|err| anyhow!("Could not parse input: {}", err))?;
values.push(value);
}
let bits = bit_count.ok_or(anyhow!(""))?;
Ok(Diagnostics {
bits,
values,
})
}
fn find_most_common_bit<'a, I: IntoIterator<Item = &'a DiagnosticValue> + Copy>(
input: I, position: usize) -> Ordering
{
let input_size = (&input).into_iter().count();
let mut bit_sum = 0;
for value in input {
let shifted = value >> position;
bit_sum += shifted & 1;
}
match bit_sum {
_ if bit_sum > (input_size - bit_sum) => Ordering::Greater,
#[allow(clippy::overflow_check_conditional)] // False positive. input_size always >= bit_sum
_ if bit_sum < (input_size - bit_sum) => Ordering::Less,
_ => Ordering::Equal,
}
}
fn find_gamma_epsilon<'a, I: IntoIterator<Item = &'a DiagnosticValue> + Copy>(input: I) ->
(DiagnosticValue, DiagnosticValue)
{
let diagnostic_count = &input.into_iter().count();
let mut gamma = 0;
let mut bit_position = 0;
let mut is_done = false;
while !is_done {
is_done = true;
let mut bit_sum = 0;
for diagnostic in input {
let shifted = diagnostic >> bit_position;
bit_sum += shifted & 1;
if shifted >> 1 != 0 {
is_done = false;
}
}
if bit_sum > diagnostic_count / 2 {
gamma += 1 << bit_position;
}
bit_position += 1;
}
let epsilon = (!gamma) ^ ((!0) << bit_position);
(gamma, epsilon)
}
fn find_oxygen_generator<'a, I>(input: I, size: usize) -> Option<DiagnosticValue>
where I: IntoIterator<Item = &'a DiagnosticValue> + Copy
{
let mut candidates: Vec<_> = input.into_iter().map(|v| v.to_owned()).collect();
for bit_shift in (0..size).rev() {
let most_common_bit = find_most_common_bit(&candidates, bit_shift);
let mut keep = Vec::new();
for candidate in &candidates {
let bit_value = (*candidate >> bit_shift) & 1;
match (most_common_bit, bit_value) {
(Ordering::Greater, 1) |
(Ordering::Less, 0) |
(Ordering::Equal, 1) => keep.push(*candidate),
(Ordering::Greater, 0) |
(Ordering::Less, 1) |
(Ordering::Equal, 0) => { },
(_, _) => panic!("Invalid bit value"),
}
}
candidates = keep;
if (&candidates).len() == 1 {
return candidates.pop();
}
}
None
}
fn find_co2_scrubber<'a, I>(input: I, size: usize) -> Option<DiagnosticValue>
where I: IntoIterator<Item = &'a DiagnosticValue> + Copy
{
let mut candidates: Vec<_> = input.into_iter().map(|v| v.to_owned()).collect();
for bit_shift in (0..size).rev() {
let most_common_bit = find_most_common_bit(&candidates, bit_shift);
let mut keep = Vec::new();
for candidate in &candidates {
let bit_value = (*candidate >> bit_shift) & 1;
match (most_common_bit, bit_value) {
(Ordering::Greater, 0) |
(Ordering::Less, 1) |
(Ordering::Equal, 0) => keep.push(*candidate),
(Ordering::Greater, 1) |
(Ordering::Less, 0) |
(Ordering::Equal, 1) => { },
(_, _) => panic!("Invalid bit value"),
}
}
candidates = keep;
if (&candidates).len() == 1 {
return candidates.pop();
}
}
None
}
fn part1(input: &Diagnostics) -> Result<(DiagnosticValue, DiagnosticValue)> {
let (gamma, epsilon) = find_gamma_epsilon(&input.values);
Ok((epsilon, gamma))
}
fn part2(input: &Diagnostics) -> Result<(DiagnosticValue, DiagnosticValue)> {
let oxygen_generator = find_oxygen_generator(&input.values, input.bits)
.ok_or(anyhow!("Could not find diagnostics for Oxygen generator."))?;
let co2_scrubber = find_co2_scrubber(&input.values, input.bits)
.ok_or(anyhow!("Could not find diagnostics for CO2 scrubber."))?;
Ok((oxygen_generator, co2_scrubber))
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or(anyhow!("Missing input filename"))?;
let input = read_input(filename).context("Could not read input")?;
if do_part_1 {
let (epsilon, gamma) = part1(&input).context("No solution for part 1")?;
let solution = epsilon * gamma;
println!("Part1, epsilon: {}, gamma: {}. Door answer: {}", epsilon, gamma, solution);
}
if do_part_2 {
let (oxygen, co2) = part2(&input).context("No solution for part 1")?;
let solution = oxygen * co2;
println!("Part2, O₂ code: {}, CO₂ code: {}. Door answer: {}", oxygen, co2, solution);
}
Ok(())
}
|
