我正在玩Python中的一些玩具代码。但不知何故无法通过。我在Tree数据结构中使用递归来生成从特定节点到每个子叶节点的路径。
递归函数背后的想法是有一个列表,它将收集到单个叶节点的每个路径,然后收集另一个列表中的每个路径。
class Tree:
def __init__(self):
self._ancestors = []
self._store_nodes = {}
def add_node(self, node):
assert isinstance(node, Node)
self._store_nodes[node.name] = node
def get_c_path(self, node):
subpath = []
path = []
path = self.ret_path(node, subpath, path)
return path
## recursive function to fetch paths
def ret_path(self, node, subpath=[], pathstore=[]):
if len(node.children) == 0:
pathstore.append(subpath)
return
else:
for c in node.children:
subpath.append(c)
self.ret_path(c, subpath, pathstore)
class Node(object):
def __init__(self, name=''):
self._name = name
self._children = set([])
self._parents = set([])
@property
def name(self):
return self._name
@property
def children(self):
return self._children
@property
def parents(self):
return self._parents
def add_child(self, node):
assert isinstance(node, Node)
self._children.add(node)
def add_parent(self, node):
assert isinstance(node, Node)
self._parents.add(node)
if __name__ == '__main__':
node_store = {1 : [2,3,4,5,6], 6 : [7,2,8,9,5], 2 : [10,11,5], 12 : [13,14,15,16], 5 : [21,22,23]}
tree = Tree()
## build the tree and set parents and children of each node
for k, v in node_store.items():
parent_node = None
if k in tree._store_nodes:
parent_node = tree._store_nodes[k]
else:
parent_node = Node(k)
tree.add_node(parent_node)
for c in v:
child_node = None
if c in tree._store_nodes:
child_node = tree._store_nodes[c]
else:
child_node = Node(c)
tree.add_node(child_node)
parent_node.add_child(child_node)
child_node.add_parent(parent_node)
print '-------------'
path = tree.get_c_path(tree._store_nodes[2])
for p in path:
for t in p:
print t.name
print "-----"
我期望的结果是Node-2的列表列表如下:
path = [[10], [11], [5, 21], [5, 22], [5, 23]]
如何更正递归函数?
答案 0 :(得分:0)
这是实现这一目标的两种方法。我不太确定如何修复你的结构;从头开始似乎更容易。
def get_c_path(self, node):
branches = [[c] for c in node.children]
expanded = self.expand_branches(branches)
while branches != expanded:
branches = expanded
expanded = self.expand_branches(expanded)
return expanded
def expand_branches(self, branches):
new_branches = []
for branch in branches:
last_node = branch[-1]
if last_node.children:
for child in last_node.children:
new_branches.append(branch + [child])
else:
new_branches.append(branch)
return new_branches