///<summary>
///creates a lookup table encoding the shortest path info between each
///node in a graph to every other
///</summary>
///<param name="graph"></param>
///<returns></returns>
public static List<List<int>> CreateAllPairsTable(SparseGraph graph)
{
const int noPath = -1;
List<int> row = new List<int>(graph.NumNodes);
for (int i = 0; i < row.Count; i++)
{
row[i] = noPath;
}
List<List<int>> shortestPaths =
new List<List<int>>(graph.NumNodes);
for (int i = 0; i < shortestPaths.Count; i++)
{
shortestPaths[i] = new List<int>(row);
}
for (int source = 0; source < graph.NumNodes; ++source)
{
//calculate the SPT for this node
GraphSearchDijkstra search =
new GraphSearchDijkstra(graph, source);
List<NavGraphEdge> spt = search.SpanningTree;
//now we have the SPT it's easy to work backwards through it to
//find the shortest paths from each node to this source node
for (int target = 0; target < graph.NumNodes; ++target)
{
//if the source node is the same as the target just set to
//target
if (source == target)
{
shortestPaths[source][target] = target;
}
else
{
int nd = target;
while ((nd != source) && (spt[nd] != null))
{
shortestPaths[spt[nd].From][target] = nd;
nd = spt[nd].From;
}
}
}
}
return shortestPaths;
}
///<summary>
///creates a lookup table of the cost associated from traveling from one
///node to every other
///</summary>
///<param name="graph"></param>
///<returns></returns>
public static List<List<float>> CreateAllPairsCostsTable(
SparseGraph graph)
{
//create a two dimensional vector
List<List<float>> pathCosts =
new List<List<float>>(graph.NumNodes);
for (int i = 0; i < graph.NumNodes; i++)
{
pathCosts.Add(new List<float>(graph.NumNodes));
for (int j = 0; j < graph.NumNodes; j++)
{
pathCosts[i].Add(0);
}
}
for (int source = 0; source < graph.NumNodes; ++source)
{
//do the search
GraphSearchDijkstra search =
new GraphSearchDijkstra(graph, source);
//iterate through every node in the graph and grab the cost to
//travel to that node
for (int target = 0; target < graph.NumNodes; ++target)
{
if (source != target)
{
pathCosts[source][target] =
search.GetCostToNode(target);
}
}
}
return pathCosts;
}
