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#[error("Indeterminate value in filter; ran off the end")] + IndeterminateValue, +} + +#[derive(Clone, Debug, PartialEq)] +struct Datum(Vec); + +impl FromStr for Datum { + type Err = Oopsie; + + fn from_str(s: &str) -> Result { + let mut retval = Vec::with_capacity(s.len()); + + for c in s.chars() { + match c { + '0' => retval.push(false), + '1' => retval.push(true), + bad => return Err(Oopsie::InvalidBit(bad)), + } + } + + Ok(Datum(retval)) + } +} + +impl fmt::Display for Datum { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + for v in self.0.iter() { + if *v { + f.write_char('1')? + } else { + f.write_char('0')? + } + } + Ok(()) + } +} + +impl From for usize { + fn from(x: Datum) -> Self { + let mut retval = 0; + + for b in x.0.iter() { + retval <<= 1; + if *b { + retval += 1; + } + } + + retval + } +} + +#[test] +fn can_read_diagnostic_data_bits() { + assert_eq!( + Ok(Datum(vec![false, false, true, false, false])), + Datum::from_str("00100") + ); + assert_eq!( + Ok(Datum(vec![true, true, true, true, false])), + Datum::from_str("11110") + ); +} + +#[derive(Debug, PartialEq)] +struct Diagnostics(Vec); + +impl<'a> From<&'a [Datum]> for Diagnostics { + fn from(data: &'a [Datum]) -> Self { + Diagnostics(data.to_vec()) + } +} + +impl FromStr for Diagnostics { + type Err = Oopsie; + + fn from_str(s: &str) -> Result { + Ok(Diagnostics(from_file_data(s)?)) + } +} + +impl Diagnostics { + fn most_common_bits(&self) -> Vec { + let total_items = self.0.len(); + let entries_per_datum = self.0.iter().map(|x| x.0.len()).min().unwrap(); + let initial_values = vec![0; entries_per_datum]; + let true_counts = self.0.iter().fold(initial_values, |acc, x| { + acc.iter() + .zip(x.0.iter()) + .map(|(count, val)| if *val { count + 1 } else { *count }) + .collect() + }); + true_counts + .iter() + .map(|count| *count >= ((total_items + 1) / 2)) + .collect() + } + + fn get_rates(&self) -> (usize, usize) { + self.most_common_bits() + .iter() + .fold((0, 0), |(gacc, eacc), most_common_is_one| { + let mut new_gamma = gacc << 1; + let mut new_epsilon = eacc << 1; + + if *most_common_is_one { + new_gamma += 1; + } else { + new_epsilon += 1; + } + + (new_gamma, new_epsilon) + }) + } + + fn rating_generator bool>(&self, f: F) -> Result { + let mut candidates = self.0.clone(); + let mut offset = 0; + + while candidates.len() > 1 { + let most_commons = Diagnostics::from(&candidates[..]).most_common_bits(); + let mut die_horribly = false; + + candidates.retain(|datum| match datum.0.get(offset) { + None => { + die_horribly = true; + false + } + Some(current_bit) => match most_commons.get(offset) { + None => { + die_horribly = true; + false + } + Some(most_common_bit) => f(*current_bit, *most_common_bit), + }, + }); + + if die_horribly { + return Err(Oopsie::IndeterminateValue); + } + + offset += 1; + } + + match candidates.pop() { + None => Err(Oopsie::IndeterminateValue), + Some(x) => Ok(usize::from(x)), + } + } + + fn o2_generator_rating(&self) -> Result { + self.rating_generator(|current, most_common| current == most_common) + } + + fn co2_scrubber_rating(&self) -> Result { + self.rating_generator(|current, most_common| current != most_common) + } +} + +#[test] +fn part1_example_works() { + let diags = Diagnostics::from_str(TEST_DATA).unwrap(); + let (gamma_rate, epsilon_rate) = diags.get_rates(); + assert_eq!(22, gamma_rate); + assert_eq!(9, epsilon_rate); +} + +#[test] +fn part2_example_works() { + let diags = Diagnostics::from_str(TEST_DATA).unwrap(); + let o2r = diags.o2_generator_rating(); + let co2r = diags.co2_scrubber_rating(); + assert_eq!(Ok(23), o2r); + assert_eq!(Ok(10), co2r); +} + +#[test] +fn regression_tests() { + let diagnostics = Diagnostics::from_str(DAY3A_DATA).unwrap(); + let (p1gamma, p1epsilon) = diagnostics.get_rates(); + assert_eq!(1491, p1gamma); + assert_eq!(2604, p1epsilon); + assert_eq!(Ok(1305), diagnostics.o2_generator_rating()); + assert_eq!(Ok(2594), diagnostics.co2_scrubber_rating()); +} + +fn day3() -> Result<(), Oopsie> { + let diagnostics = Diagnostics::from_str(DAY3A_DATA).unwrap(); + + let (gamma_rate, epsilon_rate) = diagnostics.get_rates(); + println!( + "For part #1, computed gamma rate {}, epsilon rate {}, for a power consumption {}", + gamma_rate, + epsilon_rate, + gamma_rate * epsilon_rate + ); + + let o2_generator_rating = diagnostics.o2_generator_rating()?; + let co2_scrubber_rating = diagnostics.co2_scrubber_rating()?; + println!( + "For part #2, computed O2 generator rating is {}, CO2 scrubber rating is {}, for a life support rating of {}", + o2_generator_rating, + co2_scrubber_rating, + o2_generator_rating * co2_scrubber_rating + ); + Ok(()) +} + +fn main() { + if let Err(e) = day3() { + println!("Whoops: Top-level error: {}", e); + } +}