https://adventofcode.com/2021/day/17

Launch probes to hit a target.

This solution relies on the target being in quadrant IV. You could do the math for the other quadrants, but I didn't bother!

Boundary conditions:

• x velocity must be non-negative to hit things in quadrant IV
• x velocity must not be more than xhi or the probe will miss on the first timestep.
• y velocity can't be more than ylo or it will miss on the first time step.
• y velocity can't be more than -ylo or it will skip right past the target on its way back down.