图的宽度优先算法

package WebCrawler;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Queue;

public class Graph {

    private HashMap<String, ArrayList<String>> adj; // 邻接表
    private ArrayList<String> visited;

    public Graph() {
        adj = new HashMap<String, ArrayList<String>>();
        visited = new ArrayList<String>();
    }

    public void addVertex(String v) {
        adj.put(v, new ArrayList<String>());
    }

    public void addEdge(String fromVertex, String toVertex) {
        adj.get(fromVertex).add(toVertex);
        adj.get(toVertex).add(fromVertex);
    }

    public void printGraph() {
        for (String key : adj.keySet()) {
            System.out.println(key + ": " + adj.get(key));
        }
    }

    public void broadFirstSearch(String startVertex) {

        try {
            Queue<String> q = new LinkedList<String>();
            q.add(startVertex);            //入列
            visited.add(startVertex);    
            while (!q.isEmpty()) {
                String head = q.poll();    //出列
                //System.out.println(head);
                ArrayList<String> toVisit = adj.get(head);
                for (String s : toVisit) {
                    if (!visited.contains(s)) {
                        visited.add(s);
                        q.add(s);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Graph g = new Graph();
        g.addVertex("A");
        g.addVertex("B");
        g.addVertex("C");
        g.addEdge("A", "B");
        g.addEdge("A", "C");

        g.printGraph();

        g.broadFirstSearch("A");
    }
}