tasks.mjs

// Map dangerous gas vents! In a 1000x1000 grid, identify hot spots of dangerous gas vents.

// sample data
// const input = [[[0,9],[5,9]],[[8,0],[0,8]],[[9,4],[3,4]],[[2,2],[2,1]],[[7,0],[7,4]],[[6,4],[2,0]],[[0,9],[2,9]],[[3,4],[1,4]],[[0,0],[8,8]],[[5,5],[8,2]]]

// puzzle input
import input from './input.mjs';

// only consider straight lines
function task1(input) {
  const map = Array.from(Array(1000).keys()).map(() =>
    Array.from(Array(1000).keys()).fill(0),
  );
  const filteredInput = filterOutDiagonals(input);
  filteredInput.forEach((pair) => mapPointsBetween(...pair, map));
  return map.reduce(
    (acc, row) =>
      acc + row.reduce((acc, point) => acc + (point > 1 ? 1 : 0), 0),
    0,
  );
}

// consider diagonals
function task2(input) {
  const map = Array.from(Array(1000).keys()).map(() =>
    Array.from(Array(1000).keys()).fill(0),
  );
  input.forEach((pair) => mapPointsBetween(...pair, map));
  return map.reduce(
    (acc, row) =>
      acc + row.reduce((acc, point) => acc + (point > 1 ? 1 : 0), 0),
    0,
  );
}

function filterOutDiagonals(input) {
  return input.filter(
    (pair) => pair[0][0] === pair[1][0] || pair[0][1] === pair[1][1],
  );
}

// find points between two coordinates
function mapPointsBetween(start, end, map) {
  const diffy = end[0] - start[0];
  const diffx = end[1] - start[1];

  const stepy = diffy ? diffy / Math.abs(diffy) : 0;
  const stepx = diffx ? diffx / Math.abs(diffx) : 0;

  for (
    let i = start;
    i.toString() !== end.toString();
    i[0] += stepy, i[1] += stepx
  ) {
    const point = i;
    map[point[0]][point[1]]++;
  }
  map[end[0]][end[1]]++;

  return map;
}

console.log(task1(input));
console.log(task2(input));