我在一个简单的Graph类中有这个Dijkstra算法O(n ^ 2)实现,在调试它时,输出不同于JUnit Test的预期输出,并且我找不到问题:
public void Dijkstra(T departureNode) {
initDijkstra(departureNode);
ArrayList<GraphNode<T>> V_S = fillWithoutElement(departureNode);
while (V_S.size() > 0) {
int w = chooseMinimum(D);
nodes.get(w).setVisited(true);
GraphNode<T> auxW = nodes.get(w);
V_S.remove(findOnV_S(V_S, auxW));
for(GraphNode<T> m : V_S) {
if (D[w] + weights[w][getNode(m.getElement())] < D[getNode(m.getElement())]) {
D[getNode(m.getElement())] = D[w] + weights[w][getNode(m.getElement())];
PD[getNode(m.getElement())] = w;
}
}
}
}
这是辅助方法selectMinimum():
private int chooseMinimum(double[] auxD) {
int res = 0;
double min = INFINITE;
for (int i = 0; i < auxD.length; i++) {
if (!nodes.get(i).isVisited()) {
if (auxD[i] < min) {
min = auxD[i];
res = i;
}
}
}
return res;
}
这是findOnV_S()方法:
private int findOnV_S(ArrayList<GraphNode<T>> V_S, GraphNode<T> auxW) {
int res = 0;
for(int i = 0; i < V_S.size(); i++) {
if(V_S.get(i).equals(auxW))
res = i;
}
return res;
}
这是initDijkstra()方法:
public void initDijkstra(T departureNode) {
if (!itExists(departureNode))
throw new IllegalArgumentException("Node does not exist");
D = new double[size];
PD = new int[size];
int j = getNode(departureNode);
// Initialize D
for (int i = 0; i < size; i++) {
if (edges[j][i]) {
D[i] = weights[j][i];
} else
D[i] = INFINITE;
}
// Initialize PD
for (int i = 0; i < size; i++) {
if (edges[j][i])
PD[i] = getNode(departureNode);
else
PD[i] = EMPTY;
}
initializeVisitedToFalseExceptStart(departureNode);
}
这是initializeVisitedToFalseExceptStart辅助方法:
private void initializeVisitedToFalseExceptStart(T departureNode) {
if (!itExists(departureNode))
throw new RuntimeException("Invalid node");
GraphNode<T> element = null;
for (int i = 0; i < size; i++) {
element = nodes.get(i);
if ((element.getElement()).equals(departureNode))
element.setVisited(true);
else
nodes.get(i).setVisited(false);
}
}
PD:我认为错误的方法是selectMinimum()
PD2:在下一个JUnit中,您将看到getD()将返回一个二维数组,但是Graph类中的实际D是一维数组。
PD3:这是简单的JUnit测试:
try
{
g.addNode("V1");
g.addNode("V2");
g.addNode("V3");
g.addNode("V4");
g.addNode("V5");
g.addNode("V6");
}
catch (Exception e)
{
System.out.println ("No repeated nodes are allowed" + e);
}
try
{
g.addEdge ("V1", "V2", 3.0);
g.addEdge ("V1", "V3", 4.0);
g.addEdge ("V1", "V5", 8.0);
g.addEdge ("V2", "V5", 5.0);
g.addEdge ("V3", "V5", 3.0);
g.addEdge ("V5", "V6", 3.0);
g.addEdge ("V5", "V4", 7.0);
g.addEdge ("V6", "V4", 2.0);
}
catch (Exception e)
{
System.out.println ("Starting or arrival node does not exists" + e);
}
g.Dijkstra ("V1");
assertArrayEquals (new double[][]{{Graph.INFINITE, 3.0, 4.0, 12.0, 7.0, 10.0}}, g.getD());
assertArrayEquals (new int[]{-1, 0, 0, 5, 2, 4}, g.getPD());
答案 0 :(得分:0)
我认为我找到了问题。您具有称为initializeVisitedToFalseExceptStart(departureNode)的方法 在您的initDijkstra方法中。因此,当在while循环中完成对selectedMinimum的初始调用时,您发现的是最小值,而没有考虑
我认为,如果您要删除initDijkstra方法中的该方法调用,您的算法将运行良好。