task 8.js

const input = `122202212311200210333041243104410211022242435153422552354101423030331120103122123201123013212020121
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102100020233112322130014030443133042115515544424443514351353232214340221142434234013000032002122000`;

const test_input = `30373
25512
65332
33549
35390`;

// part 1

const check_tree_is_visible = (x, y, forest, log = false) => {
  const height = forest.length;
  const width = forest[0].length;

  if (!x) return true;
  if (!y) return true;
  if (x == width - 1) return true;
  if (y == height - 1) return true;

  const current_tree = forest[y][x];

  // check all by left
  const up = forest.slice(0, y).map((l) => l[x]);
  const down = forest.slice(y + 1, height).map((l) => l[x]);
  const left = forest[y].slice(0, x);
  const right = forest[y].slice(x + 1, width);

  if (log)
    console.log({ x, y, current_tree, left, right, up, down, height, width });

  if (left.every((t) => t < current_tree)) return true;
  if (right.every((t) => t < current_tree)) return true;
  if (up.every((t) => t < current_tree)) return true;
  if (down.every((t) => t < current_tree)) return true;

  return false;
};

const solution_1 = (input) => {
  const tree_arrays = input.split("\n").map((l) => l.split(""));

  return tree_arrays.reduce(
    (acc, t_arr, y) =>
      +acc +
      +t_arr.reduce(
        (a, t, x) => +a + +check_tree_is_visible(x, y, tree_arrays),
        0
      ),
    0
  );
};

const mapped_test_case = test_input.split("\n").map((l) => l.split(""));

console.assert(
  check_tree_is_visible(1, 1, mapped_test_case) == true,
  "The top-left 5 is visible from the left and top. (It isn't visible from the right or bottom since other trees of height 5 are in the way.)"
);
console.assert(
  check_tree_is_visible(2, 1, mapped_test_case) == true,
  "The top-middle 5 is visible from the top and right"
);
console.assert(
  check_tree_is_visible(3, 1, mapped_test_case, true) == false,
  "The top-right 1 is not visible from any direction; for it to be visible, there would need to only be trees of height 0 between it and an edge."
);
console.assert(
  check_tree_is_visible(2, 2, mapped_test_case, true) == false,
  "The center 3 is not visible from any direction; for it to be visible, there would need to be only trees of at most height 2 between it and an edge."
);
console.assert(
  check_tree_is_visible(3, 2, mapped_test_case) == true,
  "The right-middle 3 is visible from the right."
);
console.assert(
  check_tree_is_visible(2, 3, mapped_test_case) == true,
  "In the bottom row, the middle 5 is visible, but the 3 and 4 are not."
);

console.assert(
  solution_1(test_input) == 21,
  "With 16 trees visible on the edge and another 5 visible in the interior, a total of 21 trees are visible in this arrangement."
);

// solution for 1st part
console.table({
  "part 1": solution_1(input),
});

// part 2

const get_tree_scenic_score = (x, y, forest, log = false) => {
  const height = forest.length;
  const width = forest[0].length;

  const current_tree = forest[y][x];

  const up = forest
    .slice(0, y)
    .map((l) => l[x])
    .reverse();
  const down = forest.slice(y + 1, height).map((l) => l[x]);
  const left = forest[y].slice(0, x).reverse();
  const right = forest[y].slice(x + 1, width);

  const highest_up = up.findIndex((t) => t >= current_tree);
  const score_up = highest_up == -1 ? up.length : highest_up + 1;

  const highest_down = down.findIndex((t) => t >= current_tree);
  const score_down = highest_down == -1 ? down.length : highest_down + 1;

  const highest_left = left.findIndex((t) => t >= current_tree);
  const score_left = highest_left == -1 ? left.length : highest_left + 1;

  const highest_right = right.findIndex((t) => t >= current_tree);
  const score_right = highest_right == -1 ? right.length : highest_right + 1;

  if (log)
    console.log({
      coords: { x, y, height, width },
      current_tree,
      dirs: { left, right, up, down },
      scores: { score_left, score_right, score_up, score_down },
    });

  return score_left * score_right * score_up * score_down;
};

console.assert(
  get_tree_scenic_score(2, 1, mapped_test_case) == 4,
  "For this tree, this is 4 (found by multiplying 1 * 1 * 2 * 2)."
);
console.assert(
  get_tree_scenic_score(2, 3, mapped_test_case) == 8,
  "This tree's scenic score is 8 (2 * 2 * 1 * 2); this is the ideal spot for the tree house."
);

const solution_2 = (input) => {
  const tree_arrays = input.split("\n").map((l) => l.split(""));

  return tree_arrays.reduce(
    (acc, t_arr, y) =>
      Math.max(
        acc,
        t_arr.reduce(
          (a, t, x) => Math.max(a, get_tree_scenic_score(x, y, tree_arrays)),
          0
        )
      ),
    0
  );
};
console.assert(
  solution_2(test_input) == 8,
  "This tree's scenic score is 8 (2 * 2 * 1 * 2); this is the ideal spot for the tree house."
);

// solution for 2nd part
console.table({
  "part 2": solution_2(input),
});