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Day 8: more optimizations 

This is getting ridiculous, but I couldn’t sleep
This commit is contained in:
kageru 2021-12-09 00:47:30 +01:00
parent 30c8e0e1ff
commit 48a392325f
Signed by: kageru
GPG Key ID: 8282A2BEA4ADA3D2
1 changed files with 16 additions and 12 deletions
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28
2021/src/bin/day08.rs
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@ -7,29 +7,31 @@ use itertools::Itertools;
use std::array;
const DAY: usize = 8;
type Parsed = Vec<([SSD; 10], [SSD; 4])>;
type Parsed = Vec<([Ssd; 10], [Ssd; 4])>;
const VALID_DISPLAYS: [SSD; 10] = [119, 36, 93, 109, 46, 107, 123, 37, 127, 111];
const VALID_DISPLAYS: [Ssd; 10] = [119, 36, 93, 109, 46, 107, 123, 37, 127, 111];
type SSD = u32;
type Ssd = u32;
struct Mapping([SSD; 7]);
struct Mapping([Ssd; 7]);
impl Mapping {
fn translate(&self, i: usize) -> SSD {
fn translate(&self, i: usize) -> Ssd {
1 << self.0[i]
}
}
fn parse(s: &str) -> SSD {
['g', 'f', 'e', 'd', 'c', 'b', 'a'].iter().map(|&c| s.contains(c)).fold(0, |acc, b| (acc | (b as SSD)) << 1) >> 1
const INPUT_MASK: [Ssd; 8] = [1, 2, 4, 8, 16, 32, 64, 128];
fn parse(s: &str) -> Ssd {
s.bytes().map(|b| INPUT_MASK[(b - b'a') as usize]).sum()
}
fn bit_at(x: SSD, n: usize) -> bool {
fn bit_at(x: Ssd, n: usize) -> bool {
(x >> n) & 1 != 0
}
fn difference(lhs: SSD, rhs: SSD) -> SSD {
fn difference(lhs: Ssd, rhs: Ssd) -> Ssd {
lhs & !rhs
}
@ -67,15 +69,17 @@ fn part2(parsed: &Parsed) -> usize {
let (e, g) = if input.iter().filter(|&&i| bit_at(i, e)).count() == 4 { (e, g) } else { (g, e) };
let mut m = [0; 7];
let mut cur = 0;
#[allow(clippy::explicit_counter_loop)] // it’s faster this way
for i in [a, b, c, d, e, f, g] {
m[i] = cur;
// We know they’re all in range, and this is actually a few % faster.
unsafe { *m.get_unchecked_mut(i) = cur };
cur += 1;
}
let mapping = Mapping(m);
output
.iter()
.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())
.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
})