aoc/year2020/
day12.rs

1//! # Rain Risk
2//!
3//! Our [`Point`] utility class comes in handy for this problem.
4//!
5//! [`Point`]: crate::util::point
6use crate::util::parse::*;
7use crate::util::point::*;
8
9type Command = (u8, i32);
10
11pub fn parse(input: &str) -> Vec<Command> {
12    input.lines().map(|line| (line.as_bytes()[0], (&line[1..]).signed())).collect()
13}
14
15pub fn part1(input: &[Command]) -> i32 {
16    let mut position = ORIGIN;
17    let mut direction = Point::new(1, 0);
18
19    for &(command, amount) in input {
20        match command {
21            b'N' => position.y -= amount,
22            b'S' => position.y += amount,
23            b'E' => position.x += amount,
24            b'W' => position.x -= amount,
25            b'L' => direction = rotate(direction, -amount),
26            b'R' => direction = rotate(direction, amount),
27            b'F' => position += direction * amount,
28            _ => unreachable!(),
29        }
30    }
31
32    position.manhattan(ORIGIN)
33}
34
35pub fn part2(input: &[Command]) -> i32 {
36    let mut position = ORIGIN;
37    let mut waypoint = Point::new(10, -1);
38
39    for &(command, amount) in input {
40        match command {
41            b'N' => waypoint.y -= amount,
42            b'S' => waypoint.y += amount,
43            b'E' => waypoint.x += amount,
44            b'W' => waypoint.x -= amount,
45            b'L' => waypoint = rotate(waypoint, -amount),
46            b'R' => waypoint = rotate(waypoint, amount),
47            b'F' => position += waypoint * amount,
48            _ => unreachable!(),
49        }
50    }
51
52    position.manhattan(ORIGIN)
53}
54
55fn rotate(point: Point, amount: i32) -> Point {
56    match amount {
57        90 | -270 => point.clockwise(),
58        180 | -180 => point * -1,
59        270 | -90 => point.counter_clockwise(),
60        _ => unreachable!(),
61    }
62}
aoc/year2020/day12.rs

aoc/year2020/
day12.rs
