/// <summary>
/// Finds negative cycle
/// </summary>
/// <param name="searchResult">Search result returned by <code>CalculateShortestPaths</code> method</param>
/// <returns></returns>
public static Path <TNode, TEdge, TVal> GetNegativeCycle <TVal>(SparseGraph <TNode, TEdge> graph,
PathLogic <TEdge, TVal> pathLogic, PathSearchResult <TNode, TEdge, TVal> searchResult)
{
var lastNodeId = -1;
foreach (var edge in graph.Edges)
{
if (pathLogic.E(searchResult.Distance[edge.From.Id], pathLogic.UnreachableValue))
{
continue;
}
var newDist = pathLogic.Relax(searchResult.Distance[edge.From.Id], edge);
if (pathLogic.Gt(searchResult.Distance[edge.To.Id], newDist))
{
searchResult.Distance[edge.To.Id] = newDist;
searchResult.Ancestors[edge.To.Id] = edge;
lastNodeId = edge.To.Id;
}
}
if (lastNodeId == -1)
{
return(null);
}
var visited = new bool[graph.NodesCnt];
for (; !visited[lastNodeId]; lastNodeId = searchResult.Ancestors[lastNodeId].From.Id)
{
visited[lastNodeId] = true;
}
var pathEdges = new List <TEdge> {
searchResult.Ancestors[lastNodeId]
};
for (var nodeId = searchResult.Ancestors[lastNodeId].From.Id; nodeId != lastNodeId; nodeId = searchResult.Ancestors[nodeId].From.Id)
{
pathEdges.Add(searchResult.Ancestors[nodeId]);
}
pathEdges.Reverse();
return(new Path <TNode, TEdge, TVal>(graph, pathLogic.ZeroValue, pathEdges));
}
private static bool ExecutePhase <TVal>(SparseGraph <TNode, TEdge> graph, PathLogic <TEdge, TVal> pathLogic,
PathSearchResult <TNode, TEdge, TVal> res)
{
var anyAction = false;
foreach (var edge in graph.Edges)
{
if (pathLogic.E(res.Distance[edge.From.Id], pathLogic.UnreachableValue))
{
continue;
}
var newDist = pathLogic.Relax(res.Distance[edge.From.Id], edge);
if (pathLogic.Gt(res.Distance[edge.To.Id], newDist) && !res.IsAncestor(edge.From.Id, edge.To.Id))
{
res.Distance[edge.To.Id] = newDist;
res.Ancestors[edge.To.Id] = edge;
anyAction = true;
}
}
return(anyAction);
}
/// <summary>
/// Calculates shortest paths from start node to all other nodes in graph
/// </summary>
/// <returns>Array of shortest path from start node to all others</returns>
public static PathSearchResult <TNode, TEdge, TVal> CalculateShortestPaths <TVal>(SparseGraph <TNode, TEdge> graph,
PathLogic <TEdge, TVal> pathLogic, TNode start)
{
return(CalculateShortestPaths(graph, pathLogic, start.Id));
}
/// <summary>
/// Calculates shortest paths from start node to all other nodes in graph
/// </summary>
/// <returns>Array of shortest path from start node to all others</returns>
public static PathSearchResult <TNode, TEdge, TVal> CalculateShortestPaths <TVal>(SparseGraph <TNode, TEdge> graph,
PathLogic <TEdge, TVal> pathLogic, int startId)
{
var res = new PathSearchResult <TNode, TEdge, TVal>(graph, startId);
var n = graph.NodesCnt;
for (var i = 0; i < n; i++)
{
res.Distance[i] = pathLogic.UnreachableValue;
}
res.Distance[startId] = pathLogic.ZeroValue;
for (var i = 0; i < n; i++)
{
if (!ExecutePhase(graph, pathLogic, res))
{
break;
}
}
res.HasNegativeCycle = ExecutePhase(graph, pathLogic, res);
return(res);
}