Fix forest generation

Author: weilycoder

cyaron/graph.py

@@ -545,9 +545,10 @@ def forest(point_count, tree_count, **kwargs):
         """
         if tree_count <= 0 or tree_count > point_count:
             raise ValueError("tree_count must be between 1 and point_count")
-        tree = list(Graph.tree(point_count, **kwargs).iterate_edges())
-        result = Graph(point_count, 0)
-        need_add = random.sample(tree, len(tree) - tree_count + 1)
+        tree = Graph.tree(point_count, **kwargs)
+        tree_edges = list(tree.iterate_edges())
+        result = Graph(point_count, tree.directed)
+        need_add = random.sample(tree_edges, len(tree_edges) - tree_count + 1)
         for edge in need_add:
             result.add_edge(edge.start, edge.end, weight=edge.weight)
         return result