// TODO: improve this part
		// No successor of the previously scheduled block works.
		// Pick a zero-degree block if we can.
		for len(zerodegree) > 0 {
			// Pop an element from the tail of the queue.
			cid := zerodegree[len(zerodegree)-1]
			zerodegree = zerodegree[:len(zerodegree)-1]
			if !scheduled[cid] {
				bid = cid
				continue blockloop
			}
		}