添加图相关内容3

Author: lovexiaoe

zhaoyu/DataStructures/Graph/Graph.java

@@ -300,4 +300,54 @@ default boolean detectCycle(){
  }
  return false;
  }
+
+ /**
+ * 查找最小生成树的辅助类
+ */
+ class CostEdge extends Edge{
+ Integer cost;
+
+ public CostEdge(int source, int target, int cost) {
+ super(source, target);
+ this.cost = cost;
+ }
+
+ @Override
+ public int compareTo(Edge o) {
+ return cost - ((CostEdge)o).cost;
+ }
+ }
+
+ /**
+ * 最小生成树。参考graph.md
+ * @param costFinder
+ * @return
+ */
+ default LinkedList<Edge> minimumSpanningTree(OneArgumentExpression<E,Integer> costFinder){
+ if(!isUndirected()){
+ throw new IllegalStateException("Spanning tree only applicable to undirected trees");
+ }
+ LinkedList<Edge> subGraph = new LinkedList<>();
+ PriorityQueue<CostEdge> edgeQueue = new PriorityQueue<>((x, y)->x.compareTo(y));
+ UnionFind<Integer> unionFind = new UnionFind<>();
+
+ //将边按照权重加入到队列中。PriorityQueue优先返回最小值。
+ this.visitAllConnectedEdges(getAllVertices().getRoot().getValue(),
+ (s,t,v)-> edgeQueue.add(new CostEdge(s,t,costFinder.compute(v))), TraversalType.DFT);
+
+ //将所有节点加入到unionFind中。
+ this.getAllVertices().traversePreOrderNonRecursive((x)-> unionFind.add(x));
+
+ //优先取权重最小的边，查看节点是否相连，未连接则进行连接。
+ while(unionFind.getPartitionCount()>1 && edgeQueue.peek()!=null){
+ Edge e = edgeQueue.poll();
+ int sGroup = unionFind.find(e.source);
+ int tGroup = unionFind.find(e.target);
+ if(sGroup!=tGroup){
+ subGraph.appendLast(e);
+ unionFind.union(e.source, e.target);
+ }
+ }
+ return subGraph;
+ }
 }