code-advent-2025/src/exercises/day_8.ts

interface Coordinate {
  x: number;
  y: number;
  z: number;
}

export default async function Playground() {
  const junction_boxes_coords = await read_junction_box_3d_positions(
    "src/exercises/assets/day_8_input.txt",
  );
  console.log(
    ">> Three largest pairings mul: ",
    get_three_largest_pairings_mul(junction_boxes_coords, 1000),
  );
  console.log(
    ">> Last pairing mul: ",
    get_last_pairing_mul(junction_boxes_coords),
  );
}

export function get_three_largest_pairings_mul(
  box_list: Coordinate[],
  max_pairings: number,
): number {
  const pairing_list = generate_n_shortest_pairings(box_list, max_pairings)
    .sort((a, b) => b.length - a.length);
  let total = 1;
  for (let i = 0; i < 3; i++) {
    total *= pairing_list[i].length;
  }

  return total;
}

export function get_last_pairing_mul(box_list: Coordinate[]): number {
  const last_pairing = get_last_pairing_circuit(box_list);
  if (last_pairing) {
    return box_list[last_pairing.a].x * box_list[last_pairing.b].x;
  }
  return 0;
}

interface DistancePairing {
  a: number;
  b: number;
  distance: number;
}

function generate_n_shortest_distances(
  box_list: Coordinate[],
  n: number,
  initial_distances?: DistancePairing[],
): DistancePairing[] {
  const distances: DistancePairing[] = initial_distances ?? [];
  for (let i = 0; i < n; i++) {
    const shortest_distance: { distance: number; pair_index: number[] } = {
      distance: Infinity, // Dirty, but it's late
      pair_index: [],
    };
    box_list.forEach((box, box_index) => {
      for (let next_i = box_index + 1; next_i < box_list.length; next_i++) {
        const next_box = box_list[next_i];
        const next_distance = calc_distance(box, next_box);

        if (
          next_distance < shortest_distance.distance &&
          !distances.some((d) =>
            (d.a === box_index && d.b === next_i) ||
            (d.b === box_index && d.a === next_i)
          )
        ) {
          shortest_distance.distance = next_distance;
          shortest_distance.pair_index = [box_index, next_i];
        }
      }
    });
    distances.push({
      a: shortest_distance.pair_index[0],
      b: shortest_distance.pair_index[1],
      distance: shortest_distance.distance,
    });
  }

  return distances;
}

function generate_n_shortest_pairings(
  box_list: Coordinate[],
  max_pairings: number,
): number[][] {
  const distance_list = generate_n_shortest_distances(box_list, max_pairings);
  const circuits: number[][] = box_list.map((_, i) => [i]);

  distance_list.forEach((distance) => {
    const a = circuits.find((c) => c.includes(distance.a));
    const b = circuits.find((c) => c.includes(distance.b));

    if (a?.length && b?.length && a !== b) {
      const to_empty_index = circuits.findIndex((c) => c.includes(distance.b));
      b.forEach((x) => a.push(x));
      circuits[to_empty_index] = [];
    }
  });

  return circuits;
}

function get_last_pairing_circuit(
  box_list: Coordinate[],
): DistancePairing | undefined {
  const INCREMENT = 10; // NOTE: to adjust computation cost, since the solution is inefficient
  const circuits: number[][] = box_list.map((_, i) => [i]);

  const is_done = (c: number[][]): boolean => {
    return c.reduce((prev, current) => {
        if (current.length > 0) {
          return prev + 1;
        }
        return prev;
      }, 0) > 1
      ? false
      : true;
  };

  let last_pairing: DistancePairing | undefined;

  let distance_list = generate_n_shortest_distances(box_list, INCREMENT);
  while (!is_done(circuits)) {
    distance_list = generate_n_shortest_distances(
      box_list,
      INCREMENT,
      distance_list,
    );
    distance_list.forEach((distance) => {
      const a = circuits.find((c) => c.includes(distance.a));
      const b = circuits.find((c) => c.includes(distance.b));

      if (a?.length && b?.length && a !== b) {
        last_pairing = {
          a: distance.a,
          b: distance.b,
          distance: distance.distance,
        };
        const to_empty_index = circuits.findIndex((c) =>
          c.includes(distance.b)
        );
        b.forEach((x) => a.push(x));
        circuits[to_empty_index] = [];
      }
    });
  }

  return last_pairing;
}

function calc_distance(a: Coordinate, b: Coordinate): number {
  return Math.sqrt(
    Math.pow(a.x - b.x, 2) + Math.pow(a.y - b.y, 2) + Math.pow(a.z - b.z, 2),
  );
}

export async function read_junction_box_3d_positions(
  path: string,
): Promise<Coordinate[]> {
  const file_txt = await Deno.readTextFile(path);
  const coordinates: Coordinate[] = [];
  file_txt.split("\n").forEach((raw_coord) => {
    if (!raw_coord.length) {
      return;
    }
    const coord_array = raw_coord.split(",");
    coordinates.push({
      x: parseInt(coord_array[0]),
      y: parseInt(coord_array[1]),
      z: parseInt(coord_array[2]),
    });
  });

  return coordinates;
}