How to tell if my player has jumped on the same platform more than once?

I have an OnCollisionEnter2D function that registers the y position of a platform that has collided with something. How can I tell if the player has jumped on a specific platform more than once?

void OnCollisionEnter2D(Collision2D coll)
	{
		foreach(ContactPoint2D contact in coll.contacts)
		{	
			currentPlatformPosition = (coll.transform.position.y);
		}
	}

Use the platform itself to keep a count inside its OnCollisionEnter function.

Make a variable outside the function and simply increment the number inside the function.