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package voronoi;
class cEdgeList {
	int n;
	cEdge head;

	cEdgeList() {
		head = null;
		n = 0;
	}

	public void InitHead(cEdge h) {
		head = new cEdge();
		head = h;
		head.next = head.prev = head;
		n = 1;
	}

	public void InsertBefore(cEdge newE, cEdge oldE) {
		if (head == null)
			InitHead(newE);
		else {
			oldE.prev.next = newE;
			newE.prev = oldE.prev;
			newE.next = oldE;
			oldE.prev = newE;
			n++;
		}
	}
	
	public void InsertBeforeHead(cEdge e) {
		if (head == null)
			InitHead(e);
		else {
			InsertBefore(e, head);
		}
	}
	
	public cEdge MakeNullEdge() {
		cEdge e = new cEdge();
		InsertBeforeHead(e);
		return e;
	}

	public void Delete(cEdge e) {

		if (head == head.next)
			head = null;
		else if (e == head)
			head = head.next;

		e.prev.next = e.next;
		e.next.prev = e.prev;
		n--;
	}

	public void ClearEdgeList() {
		if (head != null)
			head = null;
		n = 0;
	}
}