154 lines
4.2 KiB
Rust
154 lines
4.2 KiB
Rust
#![feature(test)]
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extern crate test;
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use aoc2023::{
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boilerplate,
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common::*,
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direction::{Direction, ALL_DIRECTIONS},
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position::{Position2D, PositionND},
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};
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use fnv::FnvHashSet as HashSet;
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use itertools::{Itertools, MinMaxResult};
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use std::mem::transmute;
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const DAY: usize = 10;
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type Parsed<'a> = (Pos, Vec<&'a [Pipe]>);
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type Pos = Position2D<isize>;
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#[allow(dead_code)]
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#[derive(Debug, Copy, Clone, PartialEq)]
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#[repr(u8)]
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enum Pipe {
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Vertical = b'|',
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Horizontal = b'-',
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TopRight = b'L',
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TopLeft = b'J',
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BottomRight = b'F',
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BottomLeft = b'7',
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None = b'.',
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Start = b'S',
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}
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impl Pipe {
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fn openings(self) -> [Direction; 2] {
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use self::{Direction::*, Pipe::*};
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match self {
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Vertical => [Up, Down],
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Horizontal => [Left, Right],
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TopRight => [Up, Right],
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TopLeft => [Up, Left],
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BottomRight => [Down, Right],
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BottomLeft => [Down, Left],
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None | Start => unimplemented!(),
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}
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}
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}
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fn parse_input(raw: &str) -> Parsed {
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let grid = raw.lines().rev().map(|l| unsafe { transmute::<&str, &[Pipe]>(l) }).collect_vec();
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let start = grid
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.iter()
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.zip(0..)
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.find_map(|(line, y)| line.iter().zip(0..).find_map(|(p, x)| (*p == Pipe::Start).then_some(PositionND([x, y]))))
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.unwrap();
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(start, grid)
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}
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fn step(PositionND([x, y]): Pos, dir: Direction) -> Pos {
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match dir {
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Direction::Up => PositionND([x, y + 1]),
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Direction::Right => PositionND([x + 1, y]),
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Direction::Left => PositionND([x - 1, y]),
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Direction::Down => PositionND([x, y - 1]),
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}
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}
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fn part1((start, grid): &Parsed) -> usize {
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ALL_DIRECTIONS
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.iter()
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.cloned()
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.filter_map(|mut dir| {
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let mut pos = *start;
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let mut steps = 0;
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loop {
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steps += 1;
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pos = step(pos, dir);
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if &pos == start {
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return Some(steps / 2);
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}
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dir = *grid.get(pos.0[1] as usize)?.get(pos.0[0] as usize)?.openings().iter().find(|&&o| o != !dir).unwrap();
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}
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})
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.max()
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.unwrap()
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}
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fn part2((start, grid): &Parsed) -> usize {
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let mut corners = Vec::new();
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let mut dir = Direction::Down; // I got this from my part 1 solution.
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let mut pos = *start;
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let mut points = HashSet::default();
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loop {
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pos = step(pos, dir);
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let pipe = grid[pos.0[1] as usize][pos.0[0] as usize];
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points.insert(pos);
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if matches!(pipe, Pipe::Start | Pipe::TopLeft | Pipe::TopRight | Pipe::BottomLeft | Pipe::BottomRight) {
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corners.push(pos);
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}
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if &pos == start {
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break;
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}
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dir = *pipe.openings().iter().find(|&&o| o != !dir).unwrap();
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}
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let MinMaxResult::MinMax(&ymin, &ymax) = corners.iter().map(|PositionND([y, _])| y).minmax() else { unreachable!() };
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let MinMaxResult::MinMax(&xmin, &xmax) = corners.iter().map(|PositionND([_, x])| x).minmax() else { unreachable!() };
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(ymin..=ymax)
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.flat_map(|y| (xmin..=xmax).map(move |x| PositionND([x, y])))
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.filter(|p| !points.contains(p))
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.filter(|p| is_inside(p, &corners))
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.count()
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}
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// A reimplementation of https://www.eecs.umich.edu/courses/eecs380/HANDOUTS/PROJ2/InsidePoly.html
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fn is_inside(p: &Pos, polygon: &[Pos]) -> bool {
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// Zip with next and wrap for the last element
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polygon
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.iter()
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.zip(polygon.iter().cycle().skip(1))
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.filter(|(p1, p2)| p[1] > p1[1].min(p2[1]) && p[1] <= p1[1].max(p2[1]) && p[0] <= p1[0].max(p2[0]) && p1[1] != p2[1])
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.filter(|(p1, p2)| p1[0] == p2[0] || p[0] <= (p[1] - p1[1]) * (p2[0] - p1[0]) / (p2[1] - p1[1]) + p1[0])
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.count()
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& 1
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== 1
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}
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boilerplate! {
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TEST_INPUT == "\
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-L|F7
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7S-7|
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L|7||
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-L-J|
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L|-JF"
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for tests: {
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part1: { TEST_INPUT => 4 },
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part2: {
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INPUT_P2 => 4,
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},
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},
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bench1 == 6923,
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bench2 == 529,
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bench_parse: |p: &Parsed| (p.0, p.1.len()) => (PositionND([114, 117]), 140),
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}
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#[cfg(test)]
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const INPUT_P2: &str = "\
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..........
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.S------7.
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.|F----7|.
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.||....||.
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.||....||.
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.|L-7F-J|.
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.|..||..|.
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.L--JL--J.
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..........";
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