1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110

#[cfg(feature = "visualization")]
use super::day12_renderer::Renderer;
use crate::input::Input;

pub const SHIP_POSITION_ENTITY_IDX: usize = 0;
pub const SHIP_DIRECTION_ENTITY_IDX: usize = 1;
pub const WAYPOINT_ENTITY_IDX: usize = 2;

pub fn solve(input: &mut Input) -> Result<i32, String> {
    let ship_position = (0, 0);
    let ship_direction = (1, 0);
    let waypoint = (10, -1);

    let mut entities = [ship_position, ship_direction, waypoint];
    let moved_entity_idx = input.part_values(SHIP_POSITION_ENTITY_IDX, WAYPOINT_ENTITY_IDX);
    let rotated_entity_idx = input.part_values(SHIP_DIRECTION_ENTITY_IDX, WAYPOINT_ENTITY_IDX);

    let rotation_matrices: [(i32, i32, i32, i32); 3] = [
        (0, -1, 1, 0),  //  R90 / L270
        (-1, 0, 0, -1), // R180 / L180
        (0, 1, -1, 0),  // R270 /  L90
    ];

    #[cfg(feature = "visualization")]
    let is_part_one = input.is_part_one();
    #[cfg(feature = "visualization")]
    let mut renderer = Renderer::new(&mut input.painter);
    #[cfg(feature = "visualization")]
    renderer.save_entities(entities);

    for (line_idx, line) in input.text.lines().enumerate() {
        let on_error = || {
            format!("Line {}: Invalid input - expected N|S|E|W followd by i32, or R|L followed by 90|180|270", line_idx + 1)
        };

        if line.len() < 2 {
            return Err(on_error());
        }

        let numeric_parameter = line[1..].parse::<i32>().map_err(|_| on_error())?;

        let operation = line.as_bytes()[0];
        match operation {
            b'N' => {
                entities[moved_entity_idx].1 -= numeric_parameter;
            }
            b'S' => {
                entities[moved_entity_idx].1 += numeric_parameter;
            }
            b'E' => {
                entities[moved_entity_idx].0 += numeric_parameter;
            }
            b'W' => {
                entities[moved_entity_idx].0 -= numeric_parameter;
            }
            b'R' | b'L' => {
                if !matches!(numeric_parameter, 90 | 180 | 270) {
                    return Err(on_error());
                }

                let rotation_idx = (if operation == b'L' {
                    360 - numeric_parameter
                } else {
                    numeric_parameter
                } / 90)
                    - 1;

                let rotation = rotation_matrices[rotation_idx as usize];
                let rotated = entities[rotated_entity_idx];
                entities[rotated_entity_idx] = (
                    rotated.0 * rotation.0 + rotated.1 * rotation.1,
                    rotated.0 * rotation.2 + rotated.1 * rotation.3,
                );
            }
            b'F' => {
                let direction = entities[rotated_entity_idx];
                let position = entities[SHIP_POSITION_ENTITY_IDX];
                entities[SHIP_POSITION_ENTITY_IDX] = (
                    position.0 + numeric_parameter * direction.0,
                    position.1 + numeric_parameter * direction.1,
                );
            }
            _ => {
                return Err(on_error());
            }
        }

        #[cfg(feature = "visualization")]
        renderer.save_entities(entities);
    }

    #[cfg(feature = "visualization")]
    renderer.render(is_part_one);

    let position = entities[SHIP_POSITION_ENTITY_IDX];
    Ok(position.0.abs() + position.1.abs())
}

#[test]
pub fn tests() {
    use crate::{test_part_one, test_part_two};

    let example = "F10\nN3\nF7\nR90\nF11";
    test_part_one!(example => 25);
    test_part_two!(example => 286);

    let real_input = include_str!("day12_input.txt");
    test_part_one!(real_input => 1007);
    test_part_two!(real_input => 41212);
}