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package org.psjava.algo.graph.bfs;

import org.psjava.ds.graph.Graph;
import org.psjava.ds.graph.DirectedEdge;
import org.psjava.ds.queue.Queue;
import org.psjava.ds.set.MutableSet;
import org.psjava.goods.GoodMutableSetFactory;
import org.psjava.goods.GoodQueueFactory;

public class BFS {

	private static class QueueItem {
		int depth;
		V v;

		QueueItem(int depth, V v) {
			this.depth = depth;
			this.v = v;
		}
	}

	public static > void traverse(Graph adj, Iterable startVertices, BFSVisitor visitor) {
		MutableSet discovered = GoodMutableSetFactory.getInstance().create();
		SimpleStopper stopper = new SimpleStopper();
		Queue> queue = GoodQueueFactory.getInstance().create();
		for (V v : startVertices) {
			queue.enque(new QueueItem(0, v));
			discovered.add(v);
			visitor.onDiscover(v, 0, stopper);
			if (stopper.isStopped())
				break;
		}

		while (!queue.isEmpty() && !stopper.isStopped()) {
			QueueItem cur = queue.deque();
			for (E edge : adj.getEdges(cur.v)) {
				V nextv = edge.to();
				if (!discovered.contains(nextv)) {
					discovered.add(nextv);
					visitor.onWalk(edge);
					visitor.onDiscover(nextv, cur.depth + 1, stopper);
					if (stopper.isStopped())
						break;
					queue.enque(new QueueItem(cur.depth + 1, nextv));
				}
			}
		}
	}

	private BFS() {
	}

}