//O(V+E)
void RunDFSForSCC(int node)
{
_nodeDict[node] = new NodeDiscAndLow {
DiscoveryTime = _time, EarliestAccessibleNode = _time
};
_time++;
_inStack.Add(node);
_myStack.Push(node);
foreach (var nbor in _adj[node])
{
if (_nodeDict.ContainsKey(nbor)) //Already processed
{
if (_inStack.Contains(nbor)) //BackEdge, ignore cross edges
{ //For BE u->v, EAN (Earliest Accessible Node) is Min(u.EAN,v.DiscoveryTime)
_nodeDict[node].EarliestAccessibleNode =
Math.Min(_nodeDict[node].EarliestAccessibleNode, _nodeDict[nbor].DiscoveryTime);
}
}
else
{
RunDFSForSCC(nbor);
//Update EarliestAccessibleNode
_nodeDict[node].EarliestAccessibleNode =
Math.Min(_nodeDict[node].EarliestAccessibleNode, _nodeDict[nbor].EarliestAccessibleNode);
}
}
//When exiting check if this is the start of a strongly connected component
if (_nodeDict[node].EarliestAccessibleNode == _nodeDict[node].DiscoveryTime) //Is a strongly connected component
{
var component = new List <int>();
PopFromStack(_nodeDict[node].EarliestAccessibleNode, component);
_components.Add(component);
}
}
//O(V+E)
void RunDFSForBridges(int node, int parent)
{
_nodeDict[node] = new NodeDiscAndLow {
DiscoveryTime = _time, EarliestAccessibleNode = _time
};
_time++;
if (parent != -1)
{
_parents.Add(node, parent);
}
var childrenCount = 0; //Track children count
foreach (var nbor in _adj[node])
{
childrenCount++;
if (nbor == parent)
{
continue;
}
if (_nodeDict.ContainsKey(nbor))
{
_nodeDict[node].EarliestAccessibleNode =
Math.Min(_nodeDict[node].EarliestAccessibleNode, _nodeDict[nbor].DiscoveryTime);
}
else
{
RunDFSForBridges(nbor, node);
_nodeDict[node].EarliestAccessibleNode =
Math.Min(_nodeDict[node].EarliestAccessibleNode, _nodeDict[nbor].EarliestAccessibleNode);
if (_nodeDict[nbor].EarliestAccessibleNode > _nodeDict[node].DiscoveryTime)//Bridge
{
_bridges.Add(new SharedClasses.Edge {
FromNode = node, ToNode = nbor
});
}
if (parent == -1 && childrenCount > 1) //If this is the root, and it has 2 or more children, it must be an articulation point.
{
_artPoints.Add(node);
}
else if (parent != -1 && _nodeDict[nbor].EarliestAccessibleNode >= _nodeDict[node].DiscoveryTime)//IF not root, this is an Articulation point
{
_artPoints.Add(node);
}
}
}
}
