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java - JGraphT:用另一个子树替换有向无环图中的子树

转载 作者:行者123 更新时间:2023-12-02 08:53:54 31 4
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假设我有以下两个树形图:

     a                               i
/ \ / \
b c j k
/ \ / \ / \ / \
d e f g l m n o

我需要从第一个图中提取子图 b 并将其替换到第二个图中,如下所示:

     i
/ \
j b
/ \ / \
l m d e

JGraphT 中是否有任何现有的 API 允许这样做?

最佳答案

以下答案基于以下假设:

  • 两个输入图,g1g2 都是非循环有向图(树)
  • 您想要用 g1 中的子树替换 g2 中的子树
  • g1g2 都是顶点和边不相交的,即 g1 中的顶点(边)不会出现在 中g2,反之亦然。

JGraphT 没有用于子树替换的内置方法,但实现这种方法相当简单:

/**
* Replaces the subtree rooted in root2 in graph g2 with the subtree rooted in root1 in graph g1. Graph g1 is left
* unchanged.
* @param g1 first graph
* @param g2 second graph
* @param root1 root of subtree in first graph
* @param root2 root of subtree in second graph
* @param <V> vertex type
* @param <E> edge type
*/
public static <V,E> void replaceSubtree(Graph<V, E> g1, Graph<V, E> g2, V root1, V root2){
//1. Add subtree under root1 to graph g2 as a disconnected component
BreadthFirstIterator<V, E> bfs = new BreadthFirstIterator<>(g1,root1);
g2.addVertex(bfs.next());
while (bfs.hasNext()){
V vertex=bfs.next();
V parent=bfs.getParent(vertex);
g2.addVertex(vertex);
g2.addEdge(parent,vertex,bfs.getSpanningTreeEdge(vertex));
}

//2. Get the edge (object) between root2 and its parent. A special case occurs if root2 is also the root of g2
// in which case it does not have a parent.
E treeEdge = (g2.incomingEdgesOf(root2).isEmpty() ? null : g2.incomingEdgesOf(root2).iterator().next());
V parent= (treeEdge == null ? null : Graphs.getOppositeVertex(g2, treeEdge, root2));

//3. Remove subtree rooted in vertex k
bfs = new BreadthFirstIterator<>(g2,root2);
while(bfs.hasNext())
g2.removeVertex(bfs.next());

//4. Reconnect the two components
if(parent != null)
g2.addEdge(parent, root1, treeEdge);
}

这是一些测试代码:

public static void main(String[] args){
Graph<String, DefaultEdge> g1 = new SimpleDirectedGraph<>(DefaultEdge.class);
Graphs.addAllVertices(g1, Arrays.asList("a", "b", "c", "d", "e", "f", "g"));
g1.addEdge("a", "b");
g1.addEdge("a", "c");
g1.addEdge("b", "d");
g1.addEdge("b", "e");
g1.addEdge("c", "f");
g1.addEdge("c", "g");

Graph<String, DefaultEdge> g2 = new SimpleDirectedGraph<>(DefaultEdge.class);
Graphs.addAllVertices(g2, Arrays.asList("i", "j", "k", "l", "m", "n", "o"));
g2.addEdge("i", "j");
g2.addEdge("i", "k");
g2.addEdge("j", "l");
g2.addEdge("j", "m");
g2.addEdge("k", "n");
g2.addEdge("k", "o");

replaceSubtree(g1, g2, "b", "k");

System.out.println(g2);
}
  • replaceSubtree(g1, g2, "b", "k"); 给出: ([i, j, l, m, b, d, e], [(i ,j), (j,l), (j,m), (b,d), (b,e), (i,b)])
  • replaceSubtree(g1, g2, "b", "i"); 给出: ([b, d, e], [(b,d), (b,e )])

关于java - JGraphT:用另一个子树替换有向无环图中的子树,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/60606453/

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