private static void part2(Hailstone[] hailstones) {

        Hailstone h1 = hailstones[0];
        Hailstone h2 = hailstones[1];

        int range = 500;
        for (int vx = -range; vx <= range; vx++) {
            for (int vy = -range; vy <= range; vy++) {
                for (int vz = -range; vz <= range; vz++) {

                    if (vx == 0 || vy == 0 || vz == 0) {
                        continue;
                    }

                    // Find starting point for rock that will intercept first two hailstones (x,y) on this trajectory

                    // simultaneous linear equation (from part 1):
                    // H1:  x = A + a*t   y = B + b*t
                    // H2:  x = C + c*u   y = D + d*u
                    //
                    //  t = [ d ( C - A ) - c ( D - B ) ] / ( a * d - b * c )
                    //
                    // Solve for origin of rock intercepting both hailstones in x,y:
                    //     x = A + a*t - vx*t   y = B + b*t - vy*t
                    //     x = C + c*u - vx*u   y = D + d*u - vy*u

                    long A = h1.x, a = h1.vx - vx;
                    long B = h1.y, b = h1.vy - vy;
                    long C = h2.x, c = h2.vx - vx;
                    long D = h2.y, d = h2.vy - vy;

                    // skip if division by 0
                    if (c == 0 || (a * d) - (b * c) == 0) {
                        continue;
                    }

                    // Rock intercepts H1 at time t
                    long t = (d * (C - A) - c * (D - B)) / ((a * d) - (b * c));

                    // Calculate starting position of rock from intercept point
                    long x = h1.x + h1.vx * t - vx * t;
                    long y = h1.y + h1.vy * t - vy * t;
                    long z = h1.z + h1.vz * t - vz * t;


                    // check if this rock throw will hit all hailstones

                    boolean hitall = true;
                    for (int i = 0; i < hailstones.length; i++) {

                        Hailstone h = hailstones[i];
                        long u;
                        if (h.vx != vx) {
                            u = (x - h.x) / (h.vx - vx);
                        } else if (h.vy != vy) {
                            u = (y - h.y) / (h.vy - vy);
                        } else if (h.vz != vz) {
                            u = (z - h.z) / (h.vz - vz);
                        } else {
                            throw new RuntimeException();
                        }

                        if ((x + u * vx != h.x + u * h.vx) || (y + u * vy != h.y + u * h.vy) || ( z + u * vz != h.z + u * h.vz)) {
                            hitall = false;
                            break;
                        }
                    }

                    if (hitall) {
                        System.out.printf("%d %d %d   %d %d %d   %d %n", x, y, z, vx, vy, vz, x + y + z);
                    }
                }
            }
        }
    }