GetTreeRootNId (SWIG)
'''''''''''''''''''''

.. function:: GetTreeRootNId(Graph)
   :noindex:

If *Graph* is a tree, the function returns the root id of the tree. Otherwise, it returns -1.

Parameters:

- *Graph*: directed graph (input)
    A Snap.py directed graph or a network

Return value:

- int 
    If *Graph* is a tree, the node id of the root. Otherwise, -1 is returned.


The following example shows how to get the root node id in
:class:`TNGraph` and :class:`TNEANet`::

    import snap

    Graph = snap.GenTree(snap.PNGraph, 3, 3)
    root_id = snap.GetTreeRootNId(Graph)
    print("The graph has a root id: %d" % root_id)

    Network = snap.GenTree(snap.PNEANet, 3, 3)
    root_id = snap.GetTreeRootNId(Network)
    print("The graph has a root id: %d" % root_id)