/// <summary>
/// Performs a depth-first search on the successor relation, updating the pre-order index
/// and pre-order last index relations of the graph adapter.
/// </summary>
/// <param name="a">graph adapter</param>
/// <param name="nodes">nodes to be considered</param>
/// <param name="start">start node</param>
/// <returns>all visited nodes in pre-order</returns>
public static T[] GetPreOrder <T>(this IGraphAdapter <T> a,
IList <T> nodes, T start)
{
a.PreOrderIndex.Reset(nodes, -1);
T[] result = new T[nodes.Count];
int index = 0;
a.PreOrderDFS(result, start, ref index);
// if some nodes are unreachable, the last elements of the result
// array are null. These should be eliminated:
result = result.Where(x => x != null).ToArray();
return(result);
}
private static void PreOrderDFS <T>(this IGraphAdapter <T> a,
T[] result, T node, ref int index)
{
Contract.Requires <ArgumentNullException>(a != null);
Contract.Requires <ArgumentNullException>(result != null);
Contract.Requires <ArgumentException>(index >= 0);
Contract.Requires <ArgumentException>(index < result.Length);
result[index] = node;
a.PreOrderIndex[node] = index++;
foreach (T child in a.Succs[node])
{
if (a.PreOrderIndex[child] < 0)
{
a.PreOrderDFS(result, child, ref index);
}
}
a.PreOrderLast[node] = result[index - 1];
}
