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Bitmagic

This commit is contained in:
kageru 2021-12-08 20:10:16 +01:00
parent a1f6eb888c
commit 188dd576a9
Signed by: kageru
GPG Key ID: 8282A2BEA4ADA3D2
1 changed files with 44 additions and 42 deletions
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86
2021/src/bin/day08.rs
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@ -1,34 +1,36 @@
#![feature(array_from_fn)]
#![feature(array_zip)]
#![feature(once_cell)]
#![feature(test)]
extern crate test;
use aoc2021::common::*;
use itertools::{iproduct, Itertools};
use std::{array, lazy::Lazy};
use itertools::Itertools;
use std::array;
const DAY: usize = 8;
type Parsed<'a> = Vec<([&'a str; 10], [&'a str; 4])>;
type Parsed<'a> = Vec<([SSD; 10], [SSD; 4])>;
const VALID_DISPLAYS: Lazy<[SSD; 10]> =
Lazy::new(|| ["abcefg", "cf", "acdeg", "acdfg", "bcdf", "abdfg", "abdefg", "acf", "abcdefg", "abcdfg"].map(parse));
const VALID_DISPLAYS: [SSD; 10] = [119, 36, 93, 109, 46, 107, 123, 37, 127, 111];
type SSD = [bool; 7];
type SSD = u32;
struct Mapping([char; 7]);
struct Mapping([SSD; 7]);
impl Mapping {
fn translate(&self, c: char) -> char {
self.0[(c as u8 - b'a') as usize]
fn translate(&self, i: SSD) -> SSD {
1 << self.0[i as usize]
}
}
fn parse(s: &str) -> SSD {
[s.contains('a'), s.contains('b'), s.contains('c'), s.contains('d'), s.contains('e'), s.contains('f'), s.contains('g')]
['g', 'f', 'e', 'd', 'c', 'b', 'a'].iter().map(|&c| s.contains(c)).fold(0, |acc, b| (acc | (b as SSD)) << 1) >> 1
}
fn difference(lhs: &SSD, rhs: &SSD) -> SSD {
lhs.zip(*rhs).map(|(l, r)| l && !r)
fn bit_at(x: SSD, n: SSD) -> bool {
(x >> n) & 1 != 0
}
fn difference(lhs: SSD, rhs: SSD) -> SSD {
lhs & !rhs
}
fn parse_input(raw: &str) -> Parsed {
@ -37,57 +39,52 @@ fn parse_input(raw: &str) -> Parsed {
.map(|(input, output)| {
let mut input = input.split(' ').map_into();
let mut output = output.split(' ').map_into();
(array::from_fn(|_| input.next().unwrap()), array::from_fn(|_| output.next().unwrap()))
(array::from_fn(|_| parse(input.next().unwrap())), array::from_fn(|_| parse(output.next().unwrap())))
})
.collect()
}
fn part1<'a>(parsed: &Parsed<'a>) -> usize {
parsed.iter().flat_map(|(_, output)| output).filter(|&&input| [2, 3, 4, 7].contains(&input.len())).count()
parsed.iter().flat_map(|(_, output)| output).filter(|&&input| [2, 3, 4, 7].contains(&input.count_ones())).count()
}
fn part2<'a>(parsed: &Parsed<'a>) -> usize {
parsed
.iter()
.map(|(raw_input, raw_output)| {
let [one, four, seven] = [2, 4, 3].map(|n| raw_input.iter().find(|s| s.len() == n).unwrap()).map(|&s| parse(s));
.map(|(input, raw_output)| {
let [&one, &four, &seven] = [2, 4, 3].map(|n| input.iter().find(|s| s.count_ones() == n).unwrap());
// We know the position of a for sure because it’s the only difference between 7 and 1
let a = difference(&seven, &one).iter().position(|&b| b).unwrap();
let a = (0..7).position(|n| bit_at(difference(seven, one), n)).unwrap();
// And c and f are these two (both used in 1).
// Countrary to the name, these two values are both c_or_f,
// Contrary to the name, these two values are both c_or_f,
// so we know c and f are these two, but we don’t know which is which.
let (c, f) = one.iter().positions(|&b| b).next_tuple().unwrap();
let (c, f) = (0..7).positions(|n| bit_at(one, n)).next_tuple().unwrap();
// 4 uses b, c, d, f, but we already know c and f from 1, so this leaves b and d.
let (b, d) = difference(&four, &one).iter().positions(|&b| b).next_tuple().unwrap();
let (b, d) = (0..7).positions(|n| bit_at(difference(four, one), n)).next_tuple().unwrap();
// Now e and g have to be in the remaining two positions.
let (e, g) = (0..7).filter(|n| ![a, b, c, d, f].contains(n)).next_tuple().unwrap();
debug_assert_eq!([a, b, c, d, e, f, g].into_iter().sorted().collect_vec(), (0..7).collect_vec());
// Now there are 8 possible combinations from multiplying the 3 x_or_y we constructed above.
let mapping = iproduct!([[b, d], [d, b]], [[c, f], [f, c]], [[e, g], [g, e]])
.map(|([b, d], [c, f], [e, g])| {
let mut m = [' '; 7];
m[a] = 'a';
m[b] = 'b';
m[c] = 'c';
m[d] = 'd';
m[e] = 'e';
m[f] = 'f';
m[g] = 'g';
// This is a manual implementation of itertools::iproduct specialized for 3 small
// arrays because it’s much faster this way.
let mapping = [[c, f], [f, c]]
.into_iter()
.flat_map(|[c, f]| [[c, f, b, d], [c, f, d, b]])
.flat_map(|[c, f, b, d]| [[c, f, b, d, e, g], [c, f, b, d, g, e]])
.map(|[c, f, b, d, e, g]| {
let mut m = [0; 7];
let mut cur = 0;
for i in [a, b, c, d, e, f, g] {
m[i] = cur;
cur += 1;
}
Mapping(m)
})
.find(|m| {
raw_input.iter().all(|i| {
let translated: String = i.chars().map(|n| m.translate(n)).collect();
let ssd = parse(&translated);
VALID_DISPLAYS.iter().any(|d| d == &ssd)
})
})
.find(|m| input.iter().all(|&i| VALID_DISPLAYS.contains(&(0..7).map(|n| (bit_at(i, n) as SSD) * m.translate(n)).sum())))
.unwrap();
raw_output
.iter()
.map(|i| i.chars().map(|n| mapping.translate(n)).collect::<String>())
.map(|t| parse(&t))
.map(|ssd| VALID_DISPLAYS.iter().position(|d| &ssd == d).unwrap())
.map(|&i| (0..7).map(|n| (bit_at(i, n) as SSD) * mapping.translate(n)).sum())
.map(|ssd: SSD| VALID_DISPLAYS.iter().position(|d| &ssd == d).unwrap())
.fold(0, |acc, n| (acc + n) * 10)
/ 10
})
@ -117,6 +114,11 @@ bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbg
egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce";
#[test]
fn test_parse() {
assert_eq!(parse("cgeb"), 86);
}
test!(part1() == 26);
test!(part2() == 61229);
bench!(part1() == 239);