任何人都可以帮助我理解我在这里做错了什么。我想获得图中2个给定节点之间所有路径的列表。任何帮助都会非常有用。
public class City {
final private String id;
public City(String id) {
this.id = id;
}
public City getCity() {
return node;
}
public int getCost() {
return cost;
}
}
public class Route {
private final City node;
private final int cost;
public Route(City node, int cost) {
this.node = node;
this.cost = cost;
}
}
public class Graph {
private final List<City> cities;
private final List<Route> routes;
private final Map<City, List<Route>> myGraph = new HashMap<City,List<Route>>();
private Queue<City> visited = new LinkedList<City>();
private Queue<City> beenThere = new LinkedList<City>();
public Graph(List<City> vertexes, List<Route> edges) {
this.cities = vertexes;
this.routes = edges;
}
public String toString () {
StringBuffer s = new StringBuffer();
for (City c: myGraph.keySet())
System.out.println(c + " -> " + myGraph.get(c));
System.out.println();
return s.toString();
}
public void addNew (City vertex) {
if (myGraph.containsKey(vertex))
return;
myGraph.put(vertex, new ArrayList<Route>());
}
public void add (City from, City to, int cost) {
this.addNew(from);
this.addNew(to);
myGraph.get(from).add(new Route(to,cost));
myGraph.get(to).add(new Route(from,cost));
}
public boolean contains (City vertex) {
return myGraph.containsKey(vertex);
}
// public Route returnRoute
public Queue<City> getNeighbors(City city) {
Queue<City> neighbors = new LinkedList<City>();
for (City c : myGraph.keySet()) {
String c1 = c.toString();
String city1 = city.toString();
if (c1.equals(city1))
neighbors.add(myGraph.get(c).get(0).getCity());
}
return neighbors;
}
public Queue<City> checkRoute(City node) {
Queue<City> neighbors = new LinkedList<City>();
neighbors = this.getNeighbors(node);
for (City n : neighbors)
if(visited.contains(n))
break;
else
{
visited.add(n);
beenThere.add(n);
checkRoute(n);
}
return beenThere;
}
public List<Queue<City>> BFS(Graph graph, City from, City to) {
List<Queue<City>> rute = new ArrayList<Queue<City>>();
Queue<City> toVisit = new LinkedList<City>();
toVisit.add(from);
beenThere.add(from);
while(!toVisit.isEmpty()) {
City node = toVisit.remove();
visited.add(node);
Queue<City> neighbors = new LinkedList<City>();
neighbors = this.getNeighbors(node);
while(!neighbors.isEmpty()) {
visited.add(neighbors.element());
checkRoute(neighbors.remove());
}
if (beenThere.poll().equals(to))
rute.add(beenThere);
beenThere.clear();
beenThere.add(from);
//visited.clear();
}
return rute;
}
public void ReadFile() throws IOException {
String scan;
FileReader file = new FileReader("C:\\Users\\W7\\workspace\\AI-Lab1\\graph.txt");
BufferedReader br = new BufferedReader(file);
while((scan = br.readLine()) != null) {
String[] numberString =scan.split(" ");
String from = numberString[0];
City city1 = new City(from);
String to = numberString[1];
City city2 = new City(to);
int cost = Integer.parseInt(numberString[2]);
this.add(city1, city2, cost);
}
br.close();
}
}
从文本文件graph.txt中读取城市：
Bucuresti Atena 1700
Bucuresti Budapesta 800
Paris Bucuresti 2000
Madrid Berlin 500
Kiew Moscova 800
Oslo Stokolm 590
Bucuresti Berlin 1500
Budapesta Berlin 500
public class Start {
private static List<City> nodes;
private static List<Route> edges;
private static void run () throws IOException {
nodes = new ArrayList<City>();
edges = new ArrayList<Route>();
Graph graph = new Graph(nodes, edges);
graph.ReadFile();
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
while(true) {
System.out.println("Press:");
System.out.println("[1] VIEW THE GRAPH");
System.out.println("[2] GET THE SHORTEST PATH");
try {
String s = br.readLine();
if(s.equals("exit"))
return;
int option=Integer.parseInt(s);
if (option == 1 ) {
System.out.println("The graph is:" );
System.out.println(graph);
//getGraph();
System.out.println("========================");
}
if (option == 2) {
System.out.println("\tGive source vertex : ");
String source = br.readLine();
City from = new City(source);
System.out.println("\tGive destination vertex : ");
String destination = br.readLine();
City to = new City(destination);
//getShortestPath(graph,source,destination);
System.out.println(graph.BFS(graph, from, to));
System.out.println("========================");
}
if (option == 3) {
System.out.println("Please insert city:");
String c = br.readLine();
City city = new City(c);
System.out.println(graph.getNeighbors(city));
}
}catch(IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) throws IOException {
run();
}
}
这会返回一个空列表，我不明白为什么......
答案 0 :(得分：1)
我注意到你有：
if (beenThere.poll().equals(to)) {
rute.add(beenThere);
}
要评估您自己的某个个人对象的相等性，您需要覆盖该类的hashCode()和equals()方法。
否则，两个对象永远不会相等，除非它们是内存中完全相同的对象。将这两种方法添加到City类：
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
City other = (City) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
return true;
}
另一个问题是你正在清除beenThere这也清除ArrayList中的值，因为它们都引用了内存中的同一个对象。要理解，请尝试使用以下代码来注释clear()方法以查看差异。
public static void main(String[] args) {
List<Queue<Integer>> rute = new ArrayList<Queue<Integer>>();
Queue<Integer> beenThere = new LinkedList<Integer>();
beenThere.add(1);
beenThere.add(2);
beenThere.add(3);
rute.add(beenThere);
beenThere.clear(); // run this code with this commented out to see the difference
System.out.println(rute.toString());
}
答案 1 :(得分：0)
我目前太低而无法发表评论。但是在你的Graph类中，getNeighbours方法你有一个名为 myGraph 的变量，但我无法在任何地方看到声明。