AdventOfCode/JavaScript-TypeScript/day10/grid.ts

// @link https://en.wikipedia.org/wiki/Euclidean_algorithm#Implementations
function gcd(a: number, b: number): number {
  if (b === 0) return a;
  return gcd(b, a % b);
}

/**
 * Given an x,y point, returns an angle 0-360
 * such that the top of the circle is 0, and then
 * we rotate clockwise.
 *
 * So in the below ascii circle, if you start at
 * point `0`, then you'll visit the points 1, 2, 3,
 * etc., in order.
 *
 *      9 0 1
 *     8     2
 *     7     3
 *      6 5 4
 *
 * In addition, my plane has negative y's going up
 * and positive y's going down.
 *
 *      -y ^
 *         |
 *  -x <---+---> +x
 *         |
 *      +y v
 */
function coordToAngle([x, y]: [number, number]) {
  let deg = (Math.atan2(-y, x) * 180) / Math.PI;

  // Pretty sure this can be simplified with a modulus, but can't see it
  if (deg <= 90 && deg >= 0) {
    deg = Math.abs(deg - 90);
  } else if (deg < 0) {
    deg = Math.abs(deg) + 90;
  } else {
    deg = 450 - deg;
  }

  return deg;
}

export class Grid {
  min_x: number;
  min_y: number;
  max_x: number;
  max_y: number;
  grid: number[][]; // @TODO
  asteroids: [number, number][];
  constructor(input: (1|0)[][]) {
    // `1` is an asteroid, `0` is open space
    this.grid = JSON.parse(JSON.stringify(input));
    this.asteroids = this.getAsteroidsList();

    this.min_x = 0;
    this.min_y = 0;
    this.max_x = this.grid[0].length - 1;
    this.max_y = this.grid.length - 1;
  }

  getAsteroidsList() {
    let asteroids: [number, number][] = [];
    for (let y = 0; y < this.grid.length; y++) {
      for (let x = 0; x < this.grid[y].length; x++) {
        if (this.grid[y][x]) {
          asteroids.push([x, y]);
        }
      }
    }

    return asteroids;
  }

  getVectorsFromPoint(coord: [number, number], sorted_clockwise = false) {
    let slopes: Record<string, boolean> = {};
    const [x1, y1] = coord;

    // This isn't optimized (its O(n^2)) but it works for grids of this size.
    for (let y2 = 0; y2 <= this.max_y; y2++) {
      for (let x2 = 0; x2 <= this.max_x; x2++) {
        if (x1 === x2 && y1 === y2) {
          continue;
        }

        let dy = y2 - y1;
        let dx = x2 - x1;

        let divisor = Math.abs(gcd(dy, dx));
        dy /= divisor;
        dx /= divisor;

        // Technically I'm storing inverse slopes of `x/y` but that is so my `map` function below spits out `[x, y]` coords
        slopes[`${dx}/${dy}`] = true;
      }
    }

    const vectors_to_travel = Object.keys(slopes).map((slope_str) =>
      slope_str.split("/").map((v) => parseInt(v, 10))
    ) as [number, number][];

    if (sorted_clockwise) {
      vectors_to_travel.sort((p1, p2) => {
        let p1_d = coordToAngle(p1);
        let p2_d = coordToAngle(p2);
        return p1_d - p2_d;
      });
    }

    return vectors_to_travel;
  }

  // Part one
  getAsteroidWithHighestCountInLineOfSight() {
    let best_count = -1;
    let best_coords = null;
    for (let asteroid of this.asteroids) {
      let vectors = this.getVectorsFromPoint(asteroid);
      let count = vectors
        .map((vector) => (this.getCollisionAlongVector(asteroid, vector) ? 1 : 0))
        .reduce((a: number, b) => a + b, 0);

      if (count > best_count) {
        best_count = count;
        best_coords = asteroid;
      }
    }

    return {
      best_count,
      best_coords,
    };
  }

  // Part two
  vaporizeAsteroidsFrom(start_from: [number, number] | null): number {
    if (!start_from) {
      ({ best_coords: start_from } = this.getAsteroidWithHighestCountInLineOfSight());
      const throw_error = (): [number, number] => {
        throw new Error("start_from is null");
      };
      start_from = start_from ?? throw_error();
    }

    let total_vaporized = 0;
    let vaporized = [];
    do {
      let clockwise_vectors_from_start = this.getVectorsFromPoint(start_from, true);
      for (let vector of clockwise_vectors_from_start) {
        let collision_coord = this.getCollisionAlongVector(start_from, vector);
        if (collision_coord) {
          total_vaporized++;
          this.vaporize(collision_coord);
          vaporized.push(collision_coord);
        }

        if (total_vaporized === 200) {
          let [x, y] = collision_coord ?? [0, 0];
          return x * 100 + y;
        }
      }
      // } while (this.sumAllAsteroids() > 1);
    } while (total_vaporized < 200);
    return -Infinity;
  }

  getCollisionAlongVector(from: [number, number], vector: [number, number]) {
    let collision_coord: [number, number] | null = null;
    const [x, y] = from;
    const [vx, vy] = vector;
    let new_x = x + vx;
    let new_y = y + vy;

    while (this.pointInGrid(new_x, new_y)) {
      if (this.grid[new_y][new_x]) {
        collision_coord = [new_x, new_y];
        break;
      }
      new_x += vx;
      new_y += vy;
    }

    return collision_coord;
  }

  vaporize([x, y]: [number, number]) {
    this.grid[y][x] = 0;
  }

  pointInGrid(x: number, y: number) {
    return x >= this.min_x && x <= this.max_x && y >= this.min_y && y <= this.max_y;
  }

  sumAllAsteroids() {
    let sum = 0;
    for (let y = 0; y < this.grid.length; y++) {
      for (let x = 0; x < this.grid[y].length; x++) {
        sum += this.grid[y][x];
      }
    }

    return sum;
  }
}