#enumerating all spanning trees of a directed graph
#Constructed according to https://github.com/mmozolin/FindingAllSpanningTrees/blob/master/FindAllSpanningTrees/main.cpp
#reproduced by Rongjian Liu rongjliu@foxmail.com #2018-06-11 17:11:50
#from C++ to python #run with Python 3.6
#reference: Gabow, H. N., & Myers, E. W. (1978). Finding all spanning trees of directed and undirected graphs. SIAM Journal on Computing, 7(3), 280-287.
#According to other users, this python code exist some bugs that cannot find all the spanning trees for some digraphs and needs further debug. 2022-06-21 16:37