private boolean findCycleWithBfs(Vertex current, Vertex to, Set<Vertex> ignoreSet) {
Set<Vertex> neighbours = data.get(current);
for (Vertex neighbour : neighbours) {
if (ignoreSet.contains(neighbour)) {
continue;
}
if (neighbour.equals(to)) {
return true;
}
Set<Vertex> newIgnoreSet = new HashSet<>(ignoreSet);
newIgnoreSet.add(neighbour);
boolean foundCycle = findCycleWithBfs(neighbour, to, newIgnoreSet);
if (foundCycle) {
return true;
}
}
return false;
}
/**
* Essentially uses bfs to find if there exists a cycle between two vertices of the new edge.
*
* @param edge edge for which we are looking a cycle
* @return true if there exists a cycle. false otherwise
*/
private boolean hasCycle(Edge edge) {
// if any of two vertices of the edge is not already in the disjoint set then there can't be a
// cycle either
if (!data.containsKey(edge.getFrom()) || !data.containsKey(edge.getTo())) {
return false;
}
Set<Vertex> fromNeighbours = data.get(edge.getFrom());
for (Vertex neighbour : fromNeighbours) {
boolean foundCycle = false;
if (!neighbour.equals(edge.getTo())) {
Set<Vertex> set = new HashSet<>();
set.add(neighbour);
foundCycle = findCycleWithBfs(neighbour, edge.getTo(), set);
}
if (foundCycle) {
return true;
}
}
return false;
}