/// <summary>
/// Partions the vertices based on the pivot value.
/// </summary>
/// <typeparam name="TEdgeData"></typeparam>
/// <param name="graph">The graph to sort.</param>
/// <param name="n">The hilbert accuracy.</param>
/// <param name="left">The first vertex to consider.</param>
/// <param name="right">The last vertex to consider.</param>
/// <return>The new left.</return>
private static uint SortHilbertPartition <TEdgeData>(GraphBase <TEdgeData> graph, int n, uint left, uint right)
where TEdgeData : struct, IGraphEdgeData
{ // get the pivot value.
uint start = left;
ulong pivotValue = graph.HilbertDistance(n, left);
left++;
while (true)
{
ulong leftValue = graph.HilbertDistance(n, left);
while (left <= right && leftValue <= pivotValue)
{ // move the left to the first value bigger than pivot.
left++;
leftValue = graph.HilbertDistance(n, left);
}
ulong rightValue = graph.HilbertDistance(n, right);
while (left <= right && rightValue > pivotValue)
{ // move the right to the first value smaller than pivot.
right--;
rightValue = graph.HilbertDistance(n, right);
}
if (left > right)
{ // we are done searching, left is to the right of right.
// make sure the pivot value is where it is supposed to be.
graph.Switch(start, left - 1);
return(left);
}
// swith left<->right.
graph.Switch(left, right);
}
}
/// <summary>
/// Switches the locations around for the two given vertices.
/// </summary>
/// <typeparam name="TEdgeData"></typeparam>
public static void Switch <TEdgeData>(this GraphBase <TEdgeData> graph, uint vertex1, uint vertex2)
where TEdgeData : struct, IGraphEdgeData
{
if (graph.IsDirected)
{
throw new ArgumentException("Cannot switch two vertices on a directed graph without it's reverse index.");
}
graph.Switch(vertex1, vertex2, null);
}