如何解决Tarjan的算法实现,低值节点问题
我正在尝试从图中的一组节点上执行tarjans算法,我可以成功找到“强连接的组件”,但是根节点或低值节点始终处于关闭状态,即使对于只有1个元素的SCC来说,根节点也可以与该元素不匹配 例如:
0-3 IS LOW VALUE NODE
[82-97]
529-529 IS LOW VALUE NODE
[69-81]
379-379 IS LOW VALUE NODE
[57-68]
1619-1619 IS LOW VALUE NODE
[136-137]
415-415 IS LOW VALUE NODE
[45-56]
其中顶部是低值节点,底部是组成SCC的1个元素
我当前拥有的代码在这里
package Structs;
import java.util.*;
public class TarjanSCC {
private int id;
private boolean[] onStack;
private int[] ids,low;
private Deque<Integer> stack;
private Graph<BasicBlock> graph;
private Map<BasicBlock,Integer> nodeMap;
private BasicBlock[] nodes;
private static final int UNVISITED = -1;
public TarjanSCC(Graph<BasicBlock> graph) {
this.graph = graph;
}
public void runTSCC() {
runTSCC(graph);
}
public void runTSCC(Graph<BasicBlock> nodeGraph) {
//Initialize values for sorting
this.nodes = nodeGraph.getNodes().toArray(new BasicBlock[nodeGraph.size()]);
int size = nodes.length;
this.ids = new int[size];
this.low = new int[size];
this.onStack = new boolean[size];
this.stack = new ArrayDeque<>();
this.nodeMap = new HashMap<>();
//Mark all nodes as unused,place nodes in a map so index is easily retrievable from node
for(int i = 0; i < size; i++) {
nodeMap.put(nodes[i],i);
ids[i] = UNVISITED;
}
//Invoke the DFS algorithm on each unvisited node
for(int i = 0; i < size; i++) {
if (ids[i] == UNVISITED) dfs(i,nodeGraph);
}
}
private void dfs(int at,Graph<BasicBlock> nodeGraph) {
ids[at] = low[at] = id++;
stack.push(at);
onStack[at] = true;
//Visit All Neighbours of graph and mark as visited and add to stack,for (BasicBlock edge : nodeGraph.getEdges(nodes[at])) {
int nodeArrayIndex = nodeMap.get(edge);
if (ids[nodeArrayIndex] == UNVISITED) {
dfs(nodeArrayIndex,nodeGraph);
low[at] = Math.min(low[at],low[nodeArrayIndex]);
}
else if (onStack[nodeArrayIndex]) low[at] = Math.min(low[at],nodeArrayIndex);
}
//We've visited all the neighours,lets start emptying the stack until we're at the start of the SCC
if (low[at] == ids[at]) {
List<BasicBlock> sccList = new ArrayList<>();
for (int node = stack.pop();; node = stack.pop()) {
onStack[node] = false;
sccList.add(0,nodes[node]);
if (node == at) {
System.out.println(nodes[low[at]] + " IS LOW VALUE NODE");
System.out.println(sccList);
break;
}
}
}
}
}
我怀疑问题在于设置较低的值。 我认为不需要任何其他类信息,因为从图中检索边缘没有问题
解决方法
我索引根节点错误的节点[at]是访问根节点的正确方法
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