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2021: day03: factorize

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This commit is contained in:
Antoine Martin 2021-12-03 15:33:47 +01:00
parent 03746a1dec
commit a776f56915
1 changed files with 24 additions and 38 deletions
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62
aoc2021/src/day03.rs
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@ -73,10 +73,12 @@ fn part2(input: &str) -> Result<u64> {
Ok(oxygen_generator_rating * co2_scrubber_rating)
}
/// To find oxygen generator rating, determine the most common value (0 or 1) in the current bit
/// position, and keep only numbers with that bit in that position. If 0 and 1 are equally common,
/// keep values with a 1 in the position being considered.
fn compute_oxygen_generator_rating(binary_numbers: &[&str], size: usize) -> Result<u64> {
enum FilterStrategy {
MostCommon,
LeastCommon,
}
fn filter_by_strat(binary_numbers: &[&str], size: usize, strat: FilterStrategy) -> Result<u64> {
let mut numbers = binary_numbers.to_vec();
for pos in 0..size {
@ -85,18 +87,24 @@ fn compute_oxygen_generator_rating(binary_numbers: &[&str], size: usize) -> Resu
break;
}
let most_common = if count_ones(&numbers, pos) >= ((numbers.len() + 1) / 2) {
let digit_of_interest = if count_ones(&numbers, pos) >= ((numbers.len() + 1) / 2) {
// majority of ones, or equality
'1'
match strat {
FilterStrategy::MostCommon => '1',
FilterStrategy::LeastCommon => '0',
}
} else {
// majority of zeroes
'0'
match strat {
FilterStrategy::MostCommon => '0',
FilterStrategy::LeastCommon => '1',
}
};
// TODO: use drain_filter when stable
let mut i = 0;
while i < numbers.len() {
if numbers[i].chars().nth(pos).unwrap() != most_common {
if numbers[i].chars().nth(pos).unwrap() != digit_of_interest {
numbers.remove(i);
} else {
i += 1;
@ -109,40 +117,18 @@ fn compute_oxygen_generator_rating(binary_numbers: &[&str], size: usize) -> Resu
u64::from_str_radix(numbers[0], 2).context("couldn't parse binary number")
}
/// To find oxygen generator rating, determine the most common value (0 or 1) in the current bit
/// position, and keep only numbers with that bit in that position. If 0 and 1 are equally common,
/// keep values with a 1 in the position being considered.
fn compute_oxygen_generator_rating(binary_numbers: &[&str], size: usize) -> Result<u64> {
filter_by_strat(binary_numbers, size, FilterStrategy::MostCommon)
}
/// To find CO2 scrubber rating, determine the least common value (0 or 1) in the current bit
/// position, and keep only numbers with that bit in that position. If 0 and 1 are equally
/// common, keep values with a 0 in the position being considered.
fn compute_co2_scrubber_rating(binary_numbers: &[&str], size: usize) -> Result<u64> {
let mut numbers = binary_numbers.to_vec();
for pos in 0..size {
if numbers.len() == 1 {
// only one number left, we're done!
break;
}
let least_common = if count_ones(&numbers, pos) < ((numbers.len() + 1) / 2) {
// majority of ones
'1'
} else {
// majority of zeroes, or equality
'0'
};
// TODO: use drain_filter when stable
let mut i = 0;
while i < numbers.len() {
if numbers[i].chars().nth(pos).unwrap() != least_common {
numbers.remove(i);
} else {
i += 1;
}
}
}
debug_assert_eq!(numbers.len(), 1);
u64::from_str_radix(numbers[0], 2).context("couldn't parse binary number")
filter_by_strat(binary_numbers, size, FilterStrategy::LeastCommon)
}
#[cfg(test)]