2021: day03: use lambda for part 2
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@ -73,12 +73,10 @@ fn part2(input: &str) -> Result<u64> {
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Ok(oxygen_generator_rating * co2_scrubber_rating)
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}
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enum FilterStrategy {
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MostCommon,
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LeastCommon,
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}
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fn filter_by_strat(binary_numbers: &[&str], size: usize, strat: FilterStrategy) -> Result<u64> {
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fn filter_by_strat<Strat>(binary_numbers: &[&str], size: usize, strat: Strat) -> Result<u64>
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where
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Strat: Fn(bool) -> char,
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{
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let mut numbers = binary_numbers.to_vec();
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for pos in 0..size {
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@ -87,19 +85,8 @@ fn filter_by_strat(binary_numbers: &[&str], size: usize, strat: FilterStrategy)
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break;
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}
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let digit_of_interest = if count_ones(&numbers, pos) >= ((numbers.len() + 1) / 2) {
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// majority of ones, or equality
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match strat {
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FilterStrategy::MostCommon => '1',
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FilterStrategy::LeastCommon => '0',
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}
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} else {
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// majority of zeroes
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match strat {
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FilterStrategy::MostCommon => '0',
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FilterStrategy::LeastCommon => '1',
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}
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};
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let one_is_more_common = count_ones(&numbers, pos) >= ((numbers.len() + 1) / 2);
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let digit_of_interest = strat(one_is_more_common);
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// TODO: use drain_filter when stable
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let mut i = 0;
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@ -121,14 +108,26 @@ fn filter_by_strat(binary_numbers: &[&str], size: usize, strat: FilterStrategy)
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/// position, and keep only numbers with that bit in that position. If 0 and 1 are equally common,
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/// keep values with a 1 in the position being considered.
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fn compute_oxygen_generator_rating(binary_numbers: &[&str], size: usize) -> Result<u64> {
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filter_by_strat(binary_numbers, size, FilterStrategy::MostCommon)
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filter_by_strat(binary_numbers, size, |one_is_more_common| {
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if one_is_more_common {
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'1'
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} else {
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'0'
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}
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})
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}
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/// To find CO2 scrubber rating, determine the least common value (0 or 1) in the current bit
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/// position, and keep only numbers with that bit in that position. If 0 and 1 are equally
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/// common, keep values with a 0 in the position being considered.
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fn compute_co2_scrubber_rating(binary_numbers: &[&str], size: usize) -> Result<u64> {
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filter_by_strat(binary_numbers, size, FilterStrategy::LeastCommon)
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filter_by_strat(binary_numbers, size, |one_is_more_common| {
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if one_is_more_common {
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'0'
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} else {
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'1'
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}
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})
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}
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#[cfg(test)]
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