aoc/year2018/
day10.rs

1//! # The Stars Align
2use crate::util::iter::*;
3use crate::util::parse::*;
4use crate::util::point::*;
5
6type Input = (String, i32);
7
8pub fn parse(input: &str) -> Input {
9    let (mut points, velocity): (Vec<_>, Vec<_>) = input
10        .iter_signed::<i32>()
11        .chunk::<4>()
12        .map(|[x, y, dx, dy]| (Point::new(x, y), Point::new(dx, dy)))
13        .unzip();
14
15    // Find two points traveling in opposite directions.
16    let up = velocity.iter().position(|v| v.y < 0).unwrap();
17    let down = velocity.iter().position(|v| v.y > 0).unwrap();
18
19    // Use relative velocity and position to find the time when they are 10 units apart.
20    let p = (points[up].y - points[down].y).abs();
21    let v = (velocity[up].y - velocity[down].y).abs();
22    let mut time = (p - 10) / v;
23
24    // Fast forward time.
25    tick(&mut points, &velocity, time);
26
27    // Message is 62 wide and 10 high (8 characters each 6 wide with 2 space gap between).
28    // Shrink one second at a time until area of points is exactly 620.
29    let mut area = size(&points);
30
31    while area > 620 {
32        tick(&mut points, &velocity, 1);
33        area = size(&points);
34        time += 1;
35    }
36
37    // Move top left corner of points to origin.
38    adjust(&mut points);
39
40    // Convert points to human readable string.
41    let mut grid = ['.'; 620];
42    points.iter().for_each(|p| grid[(62 * p.y + p.x) as usize] = '#');
43
44    let mut message = grid
45        .chunks_exact(62)
46        .map(|chunk| chunk.iter().collect())
47        .collect::<Vec<String>>()
48        .join("\n");
49    message.insert(0, '\n');
50
51    (message, time)
52}
53
54pub fn part1(input: &Input) -> &str {
55    &input.0
56}
57
58pub fn part2(input: &Input) -> i32 {
59    input.1
60}
61
62fn bounding_box(points: &[Point]) -> (i32, i32, i32, i32) {
63    let mut min_x = i32::MAX;
64    let mut max_x = i32::MIN;
65    let mut min_y = i32::MAX;
66    let mut max_y = i32::MIN;
67
68    for p in points {
69        min_x = min_x.min(p.x);
70        max_x = max_x.max(p.x);
71        min_y = min_y.min(p.y);
72        max_y = max_y.max(p.y);
73    }
74
75    (min_x, max_x, min_y, max_y)
76}
77
78fn size(points: &[Point]) -> i32 {
79    let (min_x, max_x, min_y, max_y) = bounding_box(points);
80    (max_x - min_x + 1) * (max_y - min_y + 1)
81}
82
83fn adjust(points: &mut [Point]) {
84    let (min_x, _, min_y, _) = bounding_box(points);
85    let top_left = Point::new(min_x, min_y);
86    points.iter_mut().for_each(|p| *p -= top_left);
87}
88
89fn tick(points: &mut [Point], velocity: &[Point], time: i32) {
90    points.iter_mut().zip(velocity.iter()).for_each(|(p, v)| {
91        *p += *v * time;
92    });
93}
aoc/year2018/day10.rs

aoc/year2018/
day10.rs
