我正在尝试用 JGraphT 实现 Prim 的最小生成树算法。它看起来怎么样？
我遇到的一个问题是 JGraphT 对所有事情的处理方式都像它所指示的那样。所以有时有必要做出一些尴尬的调用来逆转g.getEdgeSource(e)，g.getEdgeTarget(e)如果他们没有碰巧是正确的。
我最初尝试使用 JGraphT 的 Fibonacci Heap 来实现这一点，但它太难了，所以我只是做了一个常规的 PQ。
我没有将不存在的边的权重设置为无穷大，而是没有将其添加到队列中。
建议？风格问题？明显的低效率？我应该使用的代码而不是我自己的代码？
public static Graph<String, DefaultWeightedEdge> primPQ(final WeightedGraph<String, DefaultWeightedEdge> g, String root) {
Graph<String, DefaultWeightedEdge> mst = new SimpleWeightedGraph<String, DefaultWeightedEdge>(DefaultWeightedEdge.class);
Queue<DefaultWeightedEdge> pq = new PriorityQueue<DefaultWeightedEdge>(g.vertexSet().size(), new Comparator<DefaultWeightedEdge>() {
@Override
public int compare(DefaultWeightedEdge o1, DefaultWeightedEdge o2) {
if (g.getEdgeWeight(o1) < g.getEdgeWeight(o2)) {
return -1;
}
if (g.getEdgeWeight(o1) > g.getEdgeWeight(o2)) {
return 1;
}
return 0;
}
});
mst.addVertex(root);
DefaultWeightedEdge link;
for (String v : g.vertexSet()) {
link = g.getEdge(root, v);
if (link != null) {
pq.add(link);
}
}
//this is made difficult by JGraphT's assumption that everything is directed
DefaultWeightedEdge minEdge = pq.poll();
String toAdd;
String alreadyFound;
String tmp;
while (minEdge != null) {
// guessing at which is in the MST
toAdd = g.getEdgeTarget(minEdge);
alreadyFound = g.getEdgeSource(minEdge);
if (!(mst.containsVertex(toAdd) && mst.containsVertex(alreadyFound))) {
// swap if backwards
if (mst.containsVertex(toAdd)) {
tmp = toAdd;
toAdd = alreadyFound;
alreadyFound = tmp;
}
mst.addVertex(toAdd);
mst.addEdge(alreadyFound, toAdd, minEdge);
System.out.format("%s --> %s\n", g.getEdgeSource(minEdge), toAdd);
for (String v : g.vertexSet()) {
if (! mst.containsVertex(v)) {
link = g.getEdge(toAdd, v);
if (pq.contains(link)) {
g.setEdgeWeight(minEdge, Math.min(g.getEdgeWeight(minEdge), g.getEdgeWeight(link)));
}
if (link != null && ! pq.contains(link)) {
pq.add(link);
}
}
}
}
minEdge = pq.poll();
}
return mst;
}