/// <summary>
/// Breadth-first search (BFS) is an algorithm for traversing or searching tree or graph data structures.
/// Finds all vertices that can be reached by the starting vertex.
/// </summary>
/// <param name="rootVertex"></param>
/// <returns></returns>
public Dictionary <T, BfsVertexInfo <T> > BreadthFirstSearch(T rootVertex, Action <T> preVisit = null)
{
// Traversed graph information
var visitedVerticesInfo = new Dictionary <T, BfsVertexInfo <T> >();
if (!_aList.ContainsKey(rootVertex))
{
return(visitedVerticesInfo);
}
// Initialize it
foreach (var i in _aList)
{
visitedVerticesInfo[i.Key] = new BfsVertexInfo <T>();
}
// Set the distance for the root vertex
visitedVerticesInfo[rootVertex] = new BfsVertexInfo <T>()
{
Distance = 0
};
// Create a queue and add root vertex
QueueLinkedList <T> queue = new QueueLinkedList <T>();
queue.Enqueue(rootVertex);
// As long as the queue is not empty:
while (!queue.IsEmpty())
{
// Repeatedly dequeue a vertex u from the queue.
var vertex = queue.Dequeue();
Console.Write(vertex + " ");
// Trace the path
preVisit?.Invoke(vertex);
// For each neighbor v of u that has not been visited:
foreach (var neighbor in _aList[vertex])
{
if (visitedVerticesInfo[neighbor].Distance == null)
{
// Set distance to 1 greater than u's distance
visitedVerticesInfo[neighbor].Distance = visitedVerticesInfo[vertex].Distance + 1;
// Set predecessor to u
visitedVerticesInfo[neighbor].Predecessor = vertex;
// Enqueue v
queue.Enqueue(neighbor);
}
}
}
return(visitedVerticesInfo);
}
/// <summary>
/// TODO: Add a description what is going on here
/// </summary>
/// <param name="graph"></param>
/// <param name="source"></param>
/// <returns></returns>
public static BfsVertexInfo <int?>[] DoBfs(int[][] graph, int source)
{
BfsVertexInfo <int?>[] bfsInfo = new BfsVertexInfo <int?> [graph.Length];
// Initialize bfsInfo array
for (int i = 0; i < graph.Length; i++)
{
bfsInfo[i] = new BfsVertexInfo <int?>
{
Distance = null,
Predecessor = null
};
}
bfsInfo[source].Distance = 0;
var queue = new QueueLinkedList <int>();
queue.Enqueue(source);
while (!queue.IsEmpty())
{
var u = queue.Dequeue();
for (int i = 0; i < graph[u].Length; i++)
{
var v = graph[u][i];
if (bfsInfo[v].Distance == null)
{
bfsInfo[v].Distance = bfsInfo[u].Distance + 1;
bfsInfo[v].Predecessor = u;
queue.Enqueue(v);
}
}
}
return(bfsInfo);
}
