102 lines
2.7 KiB
Rust
102 lines
2.7 KiB
Rust
use crate::prelude::*;
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pub fn solution() -> Solution {
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Solution::new(Day::new(3, 2021), part_1, part_2)
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.with_expected(1092896, 4672151)
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}
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fn count_bits(input: &str) -> Result<Vec<(usize, i32)>> {
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let mut bits = HashMap::<usize, i32>::new();
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for line in input.lines() {
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for (index, bit) in line.char_indices() {
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let entry = bits.entry(index).or_default();
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match bit {
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'0' => *entry -= 1,
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'1' => *entry += 1,
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_ => return Err(eyre!("Unknown character in line: {}", line)),
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}
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}
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}
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Ok(
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bits
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.into_iter()
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.sorted_by(|(a, _), (b, _)| a.cmp(b))
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.collect(),
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)
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}
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fn part_1(input: &str) -> Result<String> {
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let bits = count_bits(input)?;
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let gamma_rate = i32::from_str_radix(
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&bits
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.clone()
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.into_iter()
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.map(|(_, bit)| if bit > 0 { '1' } else { '0' })
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.collect::<String>(),
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2,
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)?;
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let epsilon_rate = i32::from_str_radix(
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&bits
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.into_iter()
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.map(|(_, bit)| if bit < 0 { '1' } else { '0' })
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.collect::<String>(),
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2,
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)?;
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Ok((gamma_rate * epsilon_rate).to_string())
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}
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fn part_2(input: &str) -> Result<String> {
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let mut most_common_lines = input.lines().collect::<Vec<_>>();
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let mut least_common_lines = input.lines().collect::<Vec<_>>();
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let mut most_common_bits = count_bits(input)?;
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let mut least_common_bits = count_bits(input)?;
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for index in 0..most_common_bits.len() {
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if most_common_lines.len() > 1 {
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let (index, bit) = most_common_bits
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.get(index)
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.ok_or_else(|| eyre!("Could not find most common bit"))?;
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let most_common = if bit >= &0 { '1' } else { '0' };
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most_common_lines = most_common_lines
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.into_iter()
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.filter(|line| line.chars().nth(*index) == Some(most_common))
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.collect();
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most_common_bits = count_bits(&most_common_lines.join("\n"))?;
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}
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if least_common_lines.len() > 1 {
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let (index, bit) = least_common_bits
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.get(index)
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.ok_or_else(|| eyre!("Could not find least common bit"))?;
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let least_common = if bit < &0 { '1' } else { '0' };
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least_common_lines = least_common_lines
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.into_iter()
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.filter(|line| line.chars().nth(*index) == Some(least_common))
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.collect();
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least_common_bits = count_bits(&least_common_lines.join("\n"))?;
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}
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}
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let oxygen_generator_rating = i32::from_str_radix(
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most_common_lines
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.first()
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.ok_or_else(|| eyre!("Didn't find an oxygen generator rating"))?,
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2,
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)?;
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let co2_scrubber_rating = i32::from_str_radix(
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least_common_lines
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.first()
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.ok_or_else(|| eyre!("Didn't find a CO2 scrubber rating"))?,
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2,
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)?;
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Ok((oxygen_generator_rating * co2_scrubber_rating).to_string())
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}
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