Use a better way to random a forest

cyaron/graph.py

@@ -537,18 +537,19 @@ def _calc_max_edge(point_count, directed, self_loop):
 
     @staticmethod
     def forest(point_count, tree_count, **kwargs):
+        """
+        Return a forest with point_count vertexes and tree_count trees.
+        Args:
+            point_count: the count of vertexes
+            tree_count: the count of trees
+        """
         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())
-        need_delete = set(
-            i[0] for i in (Vector.random_unique_vector(tree_count - 1, [(
-                0, point_count - 2)]) if tree_count > 1 else []))
         result = Graph(point_count, 0)
-        for i in range(point_count - 1):
-            if i not in need_delete:
-                result.add_edge(tree[i].start,
-                                tree[i].end,
-                                weight=tree[i].weight)
+        need_add = random.sample(tree, len(tree) - tree_count + 1)
+        for edge in need_add:
+            result.add_edge(edge.start, edge.end, weight=edge.weight)
         return result