/// <summary>
/// Returns the shortest distances and paths between <see cref="source" /> vertex ant other vertexes.
/// </summary>
/// <param name="source">Source vertex.</param>
/// <returns>Shortest distances and paths.</returns>
/// <exception cref="ArgumentOutOfRangeException">: source less than 0 or greater than or equal the graph vertext count.</exception>
public IReadOnlyList <Vertex> GetResult(int source)
{
var n = m_weights.VertexCount;
if (source < 0 || source >= n)
{
throw new ArgumentOutOfRangeException(nameof(source));
}
// Distances and paths.
var result = new Vertex[n];
// Visited vertexes.
var visitedVertexes = new bool[n];
// Binary heap to search vertex with min distance.
var binaryHeap = m_weights is SparseGraph <int?>
?new BinaryHeap <(int v, int?d)>(new BinaryHeapComparer())
: null;
// Returns from the intermediate result a vertex with a min distance from the source vertex to it.
int GetMinFromIntermediateResult()
{
var minIndex = -1;
var minDistance = INF;
for (var i = 0; i < n; i++)
{
if (!visitedVertexes[i] &&
(minIndex == -1 || m_cmp.Compare(minDistance, result[i].Distance) > 0))
{
minIndex = i;
minDistance = result[i].Distance;
}
}
return(minIndex);
}
// Returns from the binary heap a vertex with a min distance from the source vertex to it.
int GetMinFromBinaryHeap()
{
return(binaryHeap.Count == 0
? -1
: binaryHeap.Pop().v);
}
var getMin = binaryHeap == null
? GetMinFromIntermediateResult
: (Func <int>)GetMinFromBinaryHeap;
// Initialization.
for (var i = 0; i < n; i++)
{
if (i == source)
{
// The distance from the source vertex to itself is 0.
result[i] = new Vertex(0);
}
else
{
// The distance from the source vertex to each other vertex is infinity.
result[i] = new Vertex(INF);
}
}
binaryHeap?.Push((source, 0));
while (true)
{
// 'min' is not-visited vertex with a shortest distance from the source vertex.
var min = getMin();
if (min == -1)
{
// If not found work is done.
break;
}
// Mark 'min' as visited.
visitedVertexes[min] = true;
foreach (var neighbor in m_weights.GetNeighbors(min))
{
if (neighbor.Value == INF)
{
// Vertexes are not connected.
continue;
}
if (visitedVertexes[neighbor.Number])
{
// Neighbor is visited.
continue;
}
// Alternate distance from the source vertex to the neighbor of 'min'.
var altDistance = result[min].Distance + neighbor.Value;
// Changing distance to the neighbor if a shorter path found.
if (m_cmp.Compare(result[neighbor.Number].Distance, altDistance) > 0)
{
result[neighbor.Number].Distance = altDistance;
result[neighbor.Number].Previous = min;
binaryHeap?.Push((neighbor.Number, altDistance));
}
}
}
return(result);
}
