Advent of Code 2023-24a

const IS_EXAMPLE = true;

function solve(input) {
  return process(parse(input));
}

function parse(input) {
  return input
    .split("\n")
    .map((l) => l.split(" @ ").map((e) => e.split(", ").map(Number)));
}

function process(data) {
  const MIN = IS_EXAMPLE ? 7 : 200000000000000;
  const MAX = IS_EXAMPLE ? 27 : 400000000000000;

  let count = 0;
  for (let i = 0; i < data.length; i++) {
    const [[p1x, p1y], [v1x, v1y]] = data[i];
    for (let j = i + 1; j < data.length; j++) {
      const [[p2x, p2y], [v2x, v2y]] = data[j];
      const result = intersect(
        p1x,
        p1y,
        p1x + v1x,
        p1y + v1y,
        p2x,
        p2y,
        p2x + v2x,
        p2y + v2y
      );
      if (!result) continue;
      const { x, y } = result;
      if (!(x >= MIN && x <= MAX && y >= MIN && y <= MAX)) continue;
      if (!(x - p1x > 0 === v1x > 0 && y - p1y > 0 === v1y > 0)) continue;
      if (!(x - p2x > 0 === v2x > 0 && y - p2y > 0 === v2y > 0)) continue;
      count++;
    }
  }

  return count;
}

function intersect(x1, y1, x2, y2, x3, y3, x4, y4) {
  const denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);
  if (denom == 0) return null;
  const ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denom;
  const ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denom;
  return {
    x: x1 + ua * (x2 - x1),
    y: y1 + ua * (y2 - y1),
    seg1: ua >= 0 && ua <= 1,
    seg2: ub >= 0 && ub <= 1,
  };
}