/// <summary>
/// Finds the longest path in the graph. The time limit
/// specifies the maximum duration of the search process
/// in milliseconds.
/// Returns null if no path exists.
/// </summary>
public static Path FindLongestPath(IGraph graph, long timeLimit)
{
PathList paths = new PathList();
// create initial set of paths of length zero
foreach (INode node in graph.Nodes)
{
// create a path consisting only of this node
Path path = new Path();
path.Add(node);
paths.Add(path);
// paths in which this node participates
PathStats pathStats = new PathStats();
pathStats.currentSet.Add(path, path);
node.Data = pathStats;
}
long startMillis = DateTime.Now.Ticks / 10000;
// find set of paths that are one node longer than in previous set
bool morePathsAdded = false;
do
{
morePathsAdded = false;
PathList newPaths = new PathList();
// try to extend each path in the previous set
foreach (Path path in paths)
{
INode lastNode = path.Nodes[path.Nodes.Count - 1];
foreach (ILink link in lastNode.OutLinks)
{
INode nodeToAdd = graph.Directed ?
link.Destination : link.GetOppositeNode(lastNode);
// test for cycles
PathStats testPaths = nodeToAdd.Data as PathStats;
if (testPaths.currentSet.Contains(path)) continue;
// extend the path with this node
Path newPath = new Path(path);
newPath.Add(link, nodeToAdd);
// update all nodes in the new path
foreach (INode node in newPath.Nodes)
{
PathStats nodePaths = node.Data as PathStats;
nodePaths.newSet.Add(newPath, newPath);
}
// add to the new set
morePathsAdded = true;
newPaths.Add(newPath);
}
}
if (morePathsAdded)
{
paths = newPaths;
// remove shorter paths from node associated path lists
// they are not needed in next iterations
foreach (INode node in graph.Nodes)
{
PathStats nodePaths = node.Data as PathStats;
Hashtable swap = nodePaths.currentSet;
nodePaths.currentSet = nodePaths.newSet;
nodePaths.newSet = swap;
nodePaths.newSet.Clear();
}
}
// Check time limit
if (timeLimit > 0 &&
DateTime.Now.Ticks / 10000 - startMillis > timeLimit)
break;
}
while (morePathsAdded);
// cleanup
foreach (INode node in graph.Nodes)
node.Data = null;
if (paths.Count == 0) return null;
return paths[0];
}
/// <summary>
/// Finds the longest path in the graph. The time limit
/// specifies the maximum duration of the search process
/// in milliseconds.
/// Returns null if no path exists.
/// </summary>
public static Path FindLongestPath(IGraph graph, long timeLimit)
{
PathList paths = new PathList();
// create initial set of paths of length zero
foreach (INode node in graph.Nodes)
{
// create a path consisting only of this node
Path path = new Path();
path.Add(node);
paths.Add(path);
// paths in which this node participates
PathStats pathStats = new PathStats();
pathStats.currentSet.Add(path, path);
node.Data = pathStats;
}
long startMillis = DateTime.Now.Ticks / 10000;
// find set of paths that are one node longer than in previous set
bool morePathsAdded = false;
do
{
morePathsAdded = false;
PathList newPaths = new PathList();
// try to extend each path in the previous set
foreach (Path path in paths)
{
INode lastNode = path.Nodes[path.Nodes.Count - 1];
foreach (ILink link in lastNode.OutLinks)
{
INode nodeToAdd = graph.Directed ?
link.Destination : link.GetOppositeNode(lastNode);
// test for cycles
PathStats testPaths = nodeToAdd.Data as PathStats;
if (testPaths.currentSet.Contains(path))
{
continue;
}
// extend the path with this node
Path newPath = new Path(path);
newPath.Add(link, nodeToAdd);
// update all nodes in the new path
foreach (INode node in newPath.Nodes)
{
PathStats nodePaths = node.Data as PathStats;
nodePaths.newSet.Add(newPath, newPath);
}
// add to the new set
morePathsAdded = true;
newPaths.Add(newPath);
}
}
if (morePathsAdded)
{
paths = newPaths;
// remove shorter paths from node associated path lists
// they are not needed in next iterations
foreach (INode node in graph.Nodes)
{
PathStats nodePaths = node.Data as PathStats;
Hashtable swap = nodePaths.currentSet;
nodePaths.currentSet = nodePaths.newSet;
nodePaths.newSet = swap;
nodePaths.newSet.Clear();
}
}
// Check time limit
if (timeLimit > 0 &&
DateTime.Now.Ticks / 10000 - startMillis > timeLimit)
{
break;
}
}while (morePathsAdded);
// cleanup
foreach (INode node in graph.Nodes)
{
node.Data = null;
}
if (paths.Count == 0)
{
return(null);
}
return(paths[0]);
}
