BiconnectivityInspector bug

 * JGraphT version: 1.2.0
 * Java version (java -version)/platform:  java-8-openjdk

Issue Bug in Biconnected Components Algorithm (BiconnectivityInspector.java)

Steps to reproduce (small coding example) (Simple scala code)

import java.util.function.Supplier

import org.jgrapht.graph.{DefaultEdge, SimpleDirectedGraph}
import org.jgrapht.util.SupplierUtil
import org.jgrapht.alg.connectivity.BiconnectivityInspector

import scala.collection.JavaConverters._
object bb {
  class IntSupplier (var id: Int = -1) extends Supplier[Int] {
    def get(): Int  = {
      id += 1
      id
    }
  }
  def main(args: Array[String]): Unit = {
    val g = new SimpleDirectedGraph[Int, DefaultEdge](new IntSupplier(), SupplierUtil.DEFAULT_EDGE_SUPPLIER, false)
    val vertices = List(0, 1, 2, 3, 4)
    val edges = List((0,1), (4,0), (1,4), (4,2), (4,3), (1, 3))
    for(v <- vertices){
      g.addVertex(v)
    }
    for(e <- edges){
      g.addEdge(e._1, e._2)
    }
    //println(g.edgeSet())
    val bi = new BiconnectivityInspector(g)
    val nbic = bi.getBlocks()
    for(cc <- nbic.asScala){
      println(cc.vertexSet())
    }
  }
}

outputs:

[1, 2, 3, 4]
[0, 1, 4]

Expected behaviour Crearly in the input graph (undirected version of it), the biconnected components are (0, 1, 3, 4) and (2, 4).

Other information Interestingly, if the same graph is constructed as undirected from the beginning, the algorithm works properly, so maybe the problem is related to the class AsUndirectedGraph.

[mightynull]

@jkinable yes, it does fix our issue as well, thanks for asking!

[jkinable]

@mightynull we merged the bug fix committed by @gilcu3. Could you test whether this also fixes the issue on your end, just to be certain that there are no additional hidden bugs?