94 lines
2.1 KiB
Rust
94 lines
2.1 KiB
Rust
#![feature(test)]
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extern crate test;
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use fnv::FnvHashSet as HashSet;
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use aoc2022::{boilerplate, common::*};
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const DAY: usize = 9;
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type Parsed = Vec<(u8, usize)>;
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fn parse_input(raw: &str) -> Parsed {
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raw.lines().map(|l| (l.as_bytes()[0], parse_num(&l[2..]))).collect()
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}
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fn part1(parsed: &Parsed) -> usize {
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rope::<2>(parsed)
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}
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fn part2(parsed: &Parsed) -> usize {
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rope::<10>(parsed)
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}
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fn rope<const KNOTS: usize>(parsed: &Parsed) -> usize {
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let mut knots = [(0i32, 0i32); KNOTS];
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let mut positions = HashSet::default();
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positions.insert((0, 0));
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for &(dir, n) in parsed {
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for _ in 0..n {
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match dir {
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b'U' => knots[0].1 += 1,
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b'D' => knots[0].1 -= 1,
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b'L' => knots[0].0 -= 1,
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b'R' => knots[0].0 += 1,
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_ => unreachable!(),
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}
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let mut tail_moved = true;
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for i in 0..KNOTS - 1 {
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let ro = knots[i];
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if !step_towards(&mut knots[i + 1], ro) {
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tail_moved = false;
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break;
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}
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}
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if tail_moved {
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positions.insert(knots[KNOTS - 1]);
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}
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}
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}
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positions.len()
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}
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#[inline]
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fn step_towards(tail: &mut (i32, i32), head: (i32, i32)) -> bool {
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let xdiff = head.0 - tail.0;
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let ydiff = head.1 - tail.1;
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match (xdiff, ydiff) {
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(-1 | 0 | 1, -1 | 0 | 1) => false,
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_ => {
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tail.0 += xdiff.signum();
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tail.1 += ydiff.signum();
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true
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}
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}
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}
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boilerplate! {
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TEST_INPUT == "\
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R 4\n\
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U 4\n\
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L 3\n\
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D 1\n\
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R 4\n\
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D 1\n\
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L 5\n\
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R 2\
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",
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tests: {
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part1: { TEST_INPUT => 13 },
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part2: {
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TEST_INPUT => 1,
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"R 5\n\
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U 8\n\
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L 8\n\
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D 3\n\
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R 17\n\
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D 10\n\
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L 25\n\
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U 20" => 36,
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},
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},
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bench1 == 6367,
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bench2 == 2536,
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bench_parse: Vec::len => 2000,
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}
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