128 lines
4.8 KiB
Rust
128 lines
4.8 KiB
Rust
#![feature(array_from_fn)]
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#![feature(array_zip)]
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#![feature(test)]
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extern crate test;
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use aoc2021::common::*;
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use itertools::Itertools;
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use std::array;
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const DAY: usize = 8;
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type Parsed<'a> = Vec<([SSD; 10], [SSD; 4])>;
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const VALID_DISPLAYS: [SSD; 10] = [119, 36, 93, 109, 46, 107, 123, 37, 127, 111];
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type SSD = u32;
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struct Mapping([SSD; 7]);
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impl Mapping {
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fn translate(&self, i: SSD) -> SSD {
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1 << self.0[i as usize]
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}
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}
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fn parse(s: &str) -> SSD {
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['g', 'f', 'e', 'd', 'c', 'b', 'a'].iter().map(|&c| s.contains(c)).fold(0, |acc, b| (acc | (b as SSD)) << 1) >> 1
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}
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fn bit_at(x: SSD, n: SSD) -> bool {
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(x >> n) & 1 != 0
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}
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fn difference(lhs: SSD, rhs: SSD) -> SSD {
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lhs & !rhs
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}
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fn parse_input(raw: &str) -> Parsed {
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raw.lines()
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.map(|l| l.split_once(" | ").unwrap())
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.map(|(input, output)| {
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let mut input = input.split(' ').map_into();
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let mut output = output.split(' ').map_into();
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(array::from_fn(|_| parse(input.next().unwrap())), array::from_fn(|_| parse(output.next().unwrap())))
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})
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.collect()
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}
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fn part1<'a>(parsed: &Parsed<'a>) -> usize {
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parsed.iter().flat_map(|(_, output)| output).filter(|&&input| [2, 3, 4, 7].contains(&input.count_ones())).count()
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}
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fn part2<'a>(parsed: &Parsed<'a>) -> usize {
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parsed
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.iter()
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.map(|(input, raw_output)| {
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let [&one, &four, &seven] = [2, 4, 3].map(|n| input.iter().find(|s| s.count_ones() == n).unwrap());
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// We know the position of a for sure because it’s the only difference between 7 and 1
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let a = (0..7).position(|n| bit_at(difference(seven, one), n)).unwrap();
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// And c and f are these two (both used in 1).
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// Contrary to the name, these two values are both c_or_f,
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// so we know c and f are these two, but we don’t know which is which.
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let (c, f) = (0..7).positions(|n| bit_at(one, n)).next_tuple().unwrap();
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// 4 uses b, c, d, f, but we already know c and f from 1, so this leaves b and d.
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let (b, d) = (0..7).positions(|n| bit_at(difference(four, one), n)).next_tuple().unwrap();
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// Now e and g have to be in the remaining two positions.
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let (e, g) = (0..7).filter(|n| ![a, b, c, d, f].contains(n)).next_tuple().unwrap();
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// Now there are 8 possible combinations from multiplying the 3 x_or_y we constructed above.
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// This is a manual implementation of itertools::iproduct specialized for 3 small
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// arrays because it’s much faster this way.
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let mapping = [[c, f], [f, c]]
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.into_iter()
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.flat_map(|[c, f]| [[c, f, b, d], [c, f, d, b]])
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.flat_map(|[c, f, b, d]| [[c, f, b, d, e, g], [c, f, b, d, g, e]])
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.map(|[c, f, b, d, e, g]| {
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let mut m = [0; 7];
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let mut cur = 0;
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for i in [a, b, c, d, e, f, g] {
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m[i] = cur;
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cur += 1;
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}
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Mapping(m)
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})
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.find(|m| input.iter().all(|&i| VALID_DISPLAYS.contains(&(0..7).map(|n| (bit_at(i, n) as SSD) * m.translate(n)).sum())))
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.unwrap();
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raw_output
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.iter()
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.map(|&i| (0..7).map(|n| (bit_at(i, n) as SSD) * mapping.translate(n)).sum())
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.map(|ssd: SSD| VALID_DISPLAYS.iter().position(|d| &ssd == d).unwrap())
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.fold(0, |acc, n| (acc + n) * 10)
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/ 10
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})
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.sum()
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}
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fn main() {
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let raw = read_file(DAY);
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let input = parse_input(&raw);
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println!("Part 1: {}", part1(&input));
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println!("Part 2: {}", part2(&input));
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use aoc2021::*;
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const TEST_INPUT: &str = "be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
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edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
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fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
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fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
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aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
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fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
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dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
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bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
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egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
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gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce";
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#[test]
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fn test_parse() {
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assert_eq!(parse("cgeb"), 86);
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}
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test!(part1() == 26);
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test!(part2() == 61229);
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bench!(part1() == 239);
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bench!(part2() == 946346);
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bench_input!(Vec::len => 200);
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}
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