广度优先搜索的方式模仿二叉树的层序遍历，利用一个队列存储adjacency vertex,利用white,gray and black 标示节点的三种状态。white表示未访问，gray表示已发现但为访问，也就是处于队列节点的状态，black表示已访问，也就是从队列中弹出的节点。
/*图算法*/
//breath first search
public static<T> LinkedList<T> bfs(DiGraph<T> g,T sVertex)
{
//queue stores adjaceent vertices; list stores visited vertices
LinkedQueue<T> visitQueue=new LinkedQueue();
LinkedList<T> visitList=new LinkedList<T>();
Set<T> edgeSet;
Iterator<T> edgeIter;
T currVertex=null,neighborVertex=null;
//check that starting vertex is valid
if(!g.containsVertex(sVertex))
{
throw new IllegalArgumentException("bfs():starting vertex not in the graph");
}
//color all vertices WHITE
g.colorWhite();
//initialize queue with starting vertex
visitQueue.push(sVertex);
while(!visitQueue.isEmpty())
{
//remove a vertex from the queue,color it blace and add to the list of visited vertices
currVertex=visitQueue.pop();
g.setColor(currVertex, VertexColor.BLACK);
//obtain the set of neighbors for current vertex
visitList.add(currVertex);
edgeSet=g.getNeighbors(currVertex);
//sequence through the neighbors and look for vertices
//that have not been visited
edgeIter=edgeSet.iterator();
while(edgeIter.hasNext())
{
neighborVertex=edgeIter.next();
if(g.getColor(neighborVertex)==VertexColor.WHITE)
{
//color unvisited vertex Gray and push it onto queue
g.setColor(neighborVertex, VertexColor.GRAY);
visitQueue.push(neighborVertex);
}
}
}
return visitList;
}
/*图算法*/
广度优先访问的是当前节点可达的所有节点
深度优先，模仿二叉树的后序遍历，只有在访问所有或许节点后方可访问。深度优先是一种可以区分节点发现时间和结束时间的算法，并且可以利用深度优先发现图中环的存在。深度优先返回的列表是按照每个节点结束时间相反的顺序。
public static<T> void dfsVisit(DiGraph<T> g,T sVertex,LinkedList<T>dfsList,boolean checkForCycle)
{
T neighborVertex;
Set<T> edgeSet;
//iterator to scan the adjacency set of a vertex
Iterator<T> edgeIter;
VertexColor color;
if(!g.containsVertex(sVertex))
throw new IllegalArgumentException("dfs():vertex not in the graph");
//color vertex gray note its discovery
g.setColor(sVertex,VertexColor.GRAY);
edgeSet=g.getNeighbors(sVertex);
//sequence through the adjacency set and look for vertices that are not yet discovered
//recursively call dfsVisit() for each such vertex if a vertex in the adjacency list is GRAY, the vertex was discovered during a previous call and there
//is a cycle that begins and ends at the vertex;if checkForCycle is true ,throw an Exception
edgeIter=edgeSet.iterator();
while(edgeIter.hasNext())
{
neighborVertex=edgeIter.next();
color=g.getColor(neighborVertex);
if(color==VertexColor.WHITE)
dfsVisit(g,neighborVertex,dfsList,checkForCycle);
else if(color==VertexColor.GRAY&&checkForCycle)
{
throw new IllegalPathStateException("dfsVisit():graph has a cycle!");
}
}
//finished with vertex sVertex; make it BLACK
//and add it the front of dfsList
g.setColor(sVertex,VertexColor.BLACK);
dfsList.addFirst(sVertex);
}