判断图是有向还是无向

Question

Can anyone offer some suggestions on how to write a method that returns if a graph is directed or undirected in python?

Thanks.

class DiGraph :
    def __init__ ( self ) :
        self._adj = {}
        
    def add_node ( self , u ) :
        if u not in self._adj :
            self._adj [ u ] = []
            
    def add_edge ( self , u , v , weight =1) :
        self.add_node ( u )
        self.add_node ( v )
        self._adj [ u ].append (( v , weight ) )

Answer 1

I'm not sure if this is what you are looking for but here is how I though about it.

some_graph = DiGraph()
some_graph.add_edge("a","b")
some_graph.is_directed()

This returns True since there is only an edge in one direction.

some_graph = DiGraph()
some_graph.add_edge("a","b")
some_graph.add_edge("b","a")
some_graph.is_directed()

This returns False since there are edges in both directions with the same weight.

some_graph = DiGraph()
some_graph.add_edge("a","b")
some_graph.add_edge("b","a",2)
some_graph.is_directed()

This returns True since even though there are edges in both directions they have different weights.

Full code:

class DiGraph :
    def __init__ ( self ) :
        self._adj = {}
        
    def add_node ( self , u ) :
        if u not in self._adj :
            self._adj [ u ] = []
            
    def add_edge ( self , u , v , weight =1) :
        self.add_node ( u )
        self.add_node ( v )
        self._adj [ u ].append (( v , weight ) )

    def is_directed ( self ) :
        for u, neigh in self._adj.items():
            for n in neigh:
                print("u", u, "neigh:", neigh)
                if n[0] != u and not ([(node,w) for node,w in self._adj[n[0]] if (node==u and w==n[1])]):
                    return True
        return False