Day 3!

src/bin/day3.rs

@@ -0,0 +1,227 @@
+use advent2021::from_file_data;
+use std::fmt::{self, Write};
+use std::str::FromStr;
+use thiserror::Error;
+
+#[cfg(test)]
+const TEST_DATA: &str = include_str!("../../data/day3t.txt");
+const DAY3A_DATA: &str = include_str!("../../data/day3a.txt");
+
+#[derive(Debug, Error, PartialEq)]
+enum Oopsie {
+    #[error("Invalid bit found in number: {0}")]
+    InvalidBit(char),
+    #[error("Indeterminate value in filter; ran off the end")]
+    IndeterminateValue,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+struct Datum(Vec<bool>);
+
+impl FromStr for Datum {
+    type Err = Oopsie;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        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<Datum> 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<Datum>);
+
+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<Self, Self::Err> {
+        Ok(Diagnostics(from_file_data(s)?))
+    }
+}
+
+impl Diagnostics {
+    fn most_common_bits(&self) -> Vec<bool> {
+        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<F: Fn(bool, bool) -> bool>(&self, f: F) -> Result<usize, Oopsie> {
+        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<usize, Oopsie> {
+        self.rating_generator(|current, most_common| current == most_common)
+    }
+
+    fn co2_scrubber_rating(&self) -> Result<usize, Oopsie> {
+        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);
+    }
+}