Question

我正在编写网络的递归广度优先遍历。我遇到的问题是网络通常看起来像这样：

所以我的遍历从1开始，然后遍历到2，然后是3.下一站是继续到4，所以2遍历到4.此后，3遍历到4，突然我重复工作因为两条线都试图遍历到5。

我找到的解决方案是创建一个名为self.already_traversed的列表，每次遍历一个节点时，我都会将其附加到列表中。然后，当我从节点4遍历时，我会检查以确保它已经没有遍历过。

这里的问题是我为此使用了一个实例变量，所以我需要一种方法来在第一次递归之前设置列表以及之后清理它的方法。我目前这样做的方式是：

self.already_traversed = []
self._traverse_all_nodes(start_id)
self.already_traversed = []

当然，在使用它们的函数之外变量是很糟糕的。有没有更好的方法来做到这一点，这可以放入我的遍历函数？

这是实际的代码，虽然我认为它有点密集：

def _traverse_all_nodes(self, root_authority, max_depth=6):
    """Recursively build a networkx graph

    Process is:
     - Work backwards through the authorities for self.cluster_end and all
       of its children.
     - For each authority, add it to a networkx graph, if:
        - it happened after self.cluster_start
        - it's in the Supreme Court
        - we haven't exceeded a max_depth of six cases.
        - we haven't already followed this path
    """
    g = networkx.Graph()
    if hasattr(self, 'already_traversed'):
        is_already_traversed = (root_authority.pk in self.visited_nodes)
    else:
        # First run. Create an empty list.
        self.already_traversed = []
        is_already_traversed = False

    is_past_max_depth = (max_depth <= 0)
    is_cluster_start_obj = (root_authority == self.cluster_start)
    blocking_conditions = [
        is_past_max_depth,
        is_cluster_start_obj,
        is_already_traversed,
    ]
    if not any(blocking_conditions):
        print "  No blocking conditions. Pressing on."
        self.visited_nodes.append(root_authority.pk)
        for authority in root_authority.authorities.filter(
                docket__court='scotus',
                date_filed__gte=self.cluster_start.date_filed):

            g.add_edge(root_authority.pk, authority.pk)
            # Combine our present graph with the result of the next
            # recursion
            g = networkx.compose(g, self._build_graph(
                authority,
                max_depth - 1,
            ))

    return g

def add_clusters(self):
    """Do the network analysis to add clusters to the model.

    Process is to:
     - Build a networkx graph
     - For all nodes in the graph, add them to self.clusters
    """
    self.already_traversed = []
    g = self._traverse_all_nodes(
        self.cluster_end,
        max_depth=6,
    )
    self.already_traversed = []

Answer 1

退房：

How do I pass a variable by reference?

其中包含有关如何通过引用过去列表的示例。如果您通过引用传递列表，则对函数的每次调用都将引用相同的列表。

如何干净地避免递归函数中的循环（广度优先遍历）

1 个答案: