// compute residual path from source to sink using breadth first search
// This way the Edmonds & Karp-Algorithm ensures that the shortest path
// is chosen in each iteration and thus ensures polynomial complexity.
public override List <int> ComputeResidualPath(FlowGraph network)
{
int V = network.Nodes();
bool[] visited = new bool[V]; // marks already visited nodes.
int[] pred = new int[V]; // marks the predecessor of the
// current node for the output path
// initialize
for (int v = 0; v < V; v++)
{
visited[v] = false;
}
for (int v = 0; v < V; v++)
{
pred[v] = -1;
}
visited[network.Source] = true;
Queue <int> nextNodes = new Queue <int>();
nextNodes.Enqueue(network.Source);
while (nextNodes.Count > 0)
{
int v = nextNodes.Dequeue();
foreach (Edge edge in network.Edges(v))
{
// we are only interested in paths with nonzero weights.
if ((edge.Weight() > 0) && !visited[edge.To()])
{
if (edge.To() != network.Target)
{
// If we have not yet reached the target, continue the
// search.
visited[edge.To()] = true;
pred[edge.To()] = v;
nextNodes.Enqueue(edge.To());
}
else
{
// If we have reached the target, we extract the path.
List <int> path = new List <int>();
path.Add(network.Target);
while (v != network.Source)
{
path.Add(v);
v = pred[v];
}
path.Add(network.Source);
// ... and return it
path.Reverse();
return(path);
}
}
}
}
// no path found, return null
return(null);
}
// Computes a bipartite matching in the given graph with the given partition of nodes.
// The partition is given in form of a boolean array as returned by the Partition
// function.
public static List <Edge> Matching(UndirectedGraph.Graph graph, bool[] partition)
{
List <Edge> matching = new List <Edge>();
//TODO: Implement
DirectedWeightedGraph.Graph g = new DirectedWeightedGraph.Graph(graph.Nodes() + 2);
int s = 0;
int t = g.Nodes() - 1;
for (int i = 0; i < graph.Nodes(); i++)
{
List <int> nodes = graph.AllNodes(i);
for (int j = 0; j < nodes.Count; j++)
{
g.AddEdge(i + 1, nodes[j], 1);
if (partition[i])
{
g.AddEdge(i + 1, t, 1);
}
else
{
g.AddEdge(s, i + 1, 1);
}
}
}
FlowGraph network = new FlowGraph(g, s, t);
FlowOptimizer optimizer = new EdmondsKarp.EdmondsKarp();
//optimizer.InteractiveOptimumFlow(network);
optimizer.OptimumFlow(network);
network.ComputeFlow();
for (int v = 1; v < network.Nodes() - 1; v++)
{
foreach (Edge edge in network.Edges(v))
{
if (edge.To() != s && edge.From() != t && edge.Weight() > 0)
{
matching.Add(edge);
break;
}
}
}
// Display the optimum flow
//System.Console.WriteLine("Flow is " + network.ComputeFlow());
return(matching);
}
