/// <summary>
/// The algorithm for BFS is almost exactly the same as for DFS except it uses
/// a first in, first out (FIFO) queue instead of a stack.
/// </summary>
/// <typeparam name="TNode"></typeparam>
/// <typeparam name="TEdge"></typeparam>
/// <param name="graph"></param>
/// <param name="source"></param>
/// <param name="target"></param>
/// <returns></returns>
public static SearchResult <TNode, TEdge> SearchBFS <TNode, TEdge>(this SparseGraph <TNode, TEdge> graph, int source, int target = -1)
where TNode : GraphNode
where TEdge : GraphEdge, new()
{
// reset search conditions
visited = new Visit[graph.NumNodes];
route = Enumerable.Repeat(-1, graph.NumNodes).ToArray();
SearchResult <TNode, TEdge> result = new SearchResult <TNode, TEdge> {
Source = source, Target = target
};
// Create a queue of edges
Queue <TEdge> queue = new Queue <TEdge>();
// create a dummy edge and put on the queue
TEdge dummy = new TEdge {
From = source, To = source, Cost = 0
};
queue.Enqueue(dummy);
//mark the source node as visited
visited[source] = Visit.Visited;
// while there are edges in the stack keep searching
while (queue.Count > 0)
{
// grab the next edge
TEdge next = queue.Dequeue();
// make a note of the parent of the node this edge points to
route[next.To] = next.From;
// put it on the tree. (making sure the dummy edge is not placed on the tree)
if (next != dummy)
{
result.SpanningTree.Add(next);
}
// if the target has been found the method can return success
if (next.To == target)
{
result.Found = true;
SetPathToTarget(result, source, target);
return(result);
}
// push the edges leading from the node this edge points to onto
// the queue (provided the edge does not point to a previously
// visited node)
foreach (TEdge edge in graph.Edges(next.To))
{
if (visited[edge.To] == Visit.Unvisited)
{
queue.Enqueue(edge);
visited[edge.To] = Visit.Visited;
}
}
}
// no path to target
return(result);
}
public static void Print <TNode, TEdge>(this SparseGraph <TNode, TEdge> graph)
where TNode : GraphNode
where TEdge : GraphEdge, new()
{
Console.WriteLine($"Graph is directional: {graph.IsDigraph}");
Console.WriteLine($"Graph is empty: {graph.IsEmpty}");
Console.WriteLine($"Next available slot: {graph.NextNodeIndex}");
Console.WriteLine($"Number of nodes: {graph.NumNodes}");
Console.WriteLine($"Number of active nodes: {graph.NumActiveNodes}");
Console.WriteLine($"Number of edges: {graph.NumEdges}");
Console.WriteLine("----------------------------");
Console.WriteLine("Nodes:");
foreach (TNode node in graph.Nodes)
{
Console.Write($"{node.Index}: ");
foreach (TEdge edge in graph.Edges(node.Index))
{
Console.WriteLine($"\t{edge.From}->{edge.To}::{edge.Cost}");
}
Console.WriteLine();
}
Console.WriteLine("----------------------------");
}