Implementation day 14 2021

2021/src/day14.rs

@@ -1,9 +1,124 @@
 use std::io::Read;
 
-pub fn part1(_input: &mut dyn Read) -> String {
-    todo!()
+use itertools::Itertools;
+use nom::bytes::complete::tag;
+use nom::bytes::complete::take_while;
+use nom::character::is_alphabetic;
+use nom::multi::many0;
+use nom::sequence::preceded;
+use nom::sequence::terminated;
+use nom::sequence::tuple;
+use nom::Finish;
+use nom::IResult;
+
+type Rule = (u8, u8, u8);
+
+type Pairs = [[u64; 26]; 26];
+type Rules = [[u8; 26]; 26];
+
+fn parse_input(input: &[u8]) -> IResult<&[u8], (&[u8], Vec<Rule>)> {
+    use nom::character::complete::char;
+    use nom::number::complete::u8;
+
+    let parse_start = take_while(is_alphabetic);
+    let parse_rule = tuple((u8, u8, preceded(tag(" -> "), u8)));
+
+    tuple((
+        parse_start,
+        preceded(tag("\n\n"), many0(terminated(parse_rule, char('\n')))),
+    ))(input)
 }
 
-pub fn part2(_input: &mut dyn Read) -> String {
-    todo!()
+fn read_input(input: &mut dyn Read) -> (u8, u8, Pairs, Rules) {
+    let mut buffer = Vec::new();
+    input.read_to_end(&mut buffer).unwrap();
+
+    let (initial, rules) = parse_input(&buffer).finish().unwrap().1;
+
+    let mut pairs = Pairs::default();
+
+    for window in initial.windows(2) {
+        pairs[(window[0] - b'A') as usize][(window[1] - b'A') as usize] += 1;
+    }
+
+    let mut rule_map = Rules::default();
+    for (first, second, product) in rules {
+        rule_map[(first - b'A') as usize][(second - b'A') as usize] = product - b'A';
+    }
+
+    (
+        initial[0] - b'A',
+        initial[initial.len() - 1] - b'A',
+        pairs,
+        rule_map,
+    )
+}
+
+fn update(pairs: Pairs, rules: &Rules) -> Pairs {
+    let mut new_pairs = Pairs::default();
+
+    pairs.iter().enumerate().for_each(|(first, row)| {
+        row.iter().enumerate().for_each(|(second, &count)| {
+            let product = rules[first][second] as usize;
+            new_pairs[first][product] += count;
+            new_pairs[product][second] += count;
+        })
+    });
+
+    new_pairs
+}
+
+fn parts_common(input: &mut dyn Read, rounds: usize) -> String {
+    let (first, last, mut pairs, rules) = read_input(input);
+
+    (0..rounds).for_each(|_| pairs = update(pairs, &rules));
+
+    let mut pair_counts = [0; 26];
+    pairs.iter().enumerate().for_each(|(first, row)| {
+        row.iter().enumerate().for_each(|(second, &count)| {
+            pair_counts[first] += count;
+            pair_counts[second] += count;
+        })
+    });
+
+    pair_counts[first as usize] += 1;
+    pair_counts[last as usize] += 1;
+
+    // Now everything is counted twice, so first half everything
+    let counts = pair_counts.map(|pair_count| pair_count / 2);
+
+    match counts.into_iter().filter(|&c| c != 0).minmax() {
+        itertools::MinMaxResult::NoElements => unreachable!(),
+        itertools::MinMaxResult::OneElement(_) => 0,
+        itertools::MinMaxResult::MinMax(min, max) => max - min,
+    }
+    .to_string()
+}
+
+pub fn part1(input: &mut dyn Read) -> String {
+    parts_common(input, 10)
+}
+
+pub fn part2(input: &mut dyn Read) -> String {
+    parts_common(input, 40)
+}
+
+#[cfg(test)]
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::test_implementation;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/14.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation(part1, SAMPLE, 1588);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation(part2, SAMPLE, 2188189693529u64);
+    }
 }

2021/src/samples/14.txt

@@ -0,0 +1,18 @@
+NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C