DO NOT pass the wrong-way driver. This is extremely dangerous and could result in a head-on collision.
If the wrong-way driver is approaching you, honk your horn and flash your lights to warn them. You may also want to slow down and come to a stop.
Once the wrong-way driver has passed, proceed with caution. Be sure to check your mirrors and blind spots to ensure that there are no other wrong-way drivers in the area.
Call the police to report the incident. The police can help to track down the wrong-way driver and prevent them from causing any more accidents.