remove_edge_if_dir.expected

C++的一个好库。。。现在很流行

original graph:
0 --> 3 2 3 
1 --> 3 
2 --> 0 
3 --> 2 

removing edges (0,3)
0 --> 2 
1 --> 3 
2 --> 0 
3 --> 2 
removing edge (0,2) and (3, 2)
0 --> 
1 --> 3 
2 --> 0 
3 -->