class BTNode(object):
"""A node in a binary tree."""
def __init__(self, item, left=None, right=None):
"""(BTNode, object, BTNode, BTNode) -> NoneType
Initialize this node to store item and have children left and right,
as well as depth 0.
"""
self.item = item
self.left = left
self.right = right
self.depth = 0 # the depth of this node in a tree
def __str__(self):
"""(BTNode) -> str
Return a "sideways" representation of the subtree rooted at this node,
with right subtrees above parents above left subtrees and each node on
its own line, preceded by as many TAB characters as the node's depth.
"""
# If there is a right subtree, add an extra TAB character in front of
# every node in its string representation, with an extra newline at the
# end (ready to be concatenated with self.item).
if self.right:
str_right = "\t" + str(self.right).replace("\n", "\n\t") + "\n"
else:
str_right = ""
# The string representation of self.item: if item is a string, use
# repr(item) so that quotes are included and special characters are
# treated correctly -- just like in a list; else use str(item).
if isinstance(self.item, str):
str_item = repr(self.item)
else:
str_item = str(self.item)
# If there is a left subtree, add an extra TAB character in front of
# every node in its string representation, with an extra newline at the
# beginning (ready to be concatenated with self.item).
if self.left:
str_left = "\n\t" + str(self.left).replace("\n", "\n\t")
else:
str_left = ""
# Put the right subtree above the root above the left subtree.
return str_right + str_item + str_left
def leaves_and_internals(self):
"""(BTNode) -> ([object], [object])
Return a pair of lists: (list of all the items stored in the leaves of
the subtree rooted at this node, list of all the items stored in the
internal nodes of the subtree rooted at this node).
"""
#Leaf: Doesn't have children
#Internal Node: Has children
leaf = []
internal = []
if not self.left and not self.right:
leaf.append(self.item)
if self.left is not None:
internal.append(self.item)
if self.right is not None:
self.right.leaves_and_internals()
self.left.leaves_and_internals()
elif self.right is not None:
internal.append(self.item)
self.right.leaves_and_internals()
print(leaf, internal)
return leaf, internal
BTNode 类是提供给我们的起始代码，我们无法对其进行编辑。我的职责是按照给定的文档字符串为leaves_and_intervals 编写代码。我目前唯一的问题是不知道如何使用扩展来正确递归地组合列表。
我的测试块看起来像这样：
if __name__ == "__main__":
root = BTNode(2, BTNode(4, BTNode(6, BTNode(8, None, None), None), None), None)
root.leaves_and_internals()
我的输出看起来像这样：
[8] []
[] [6]
[] [4]
[] [2]
正确的输出应该如下所示（顺序无关紧要）：
[8] [6, 4, 2]
如何正确使用扩展，以便叶子和内部不会在每次递归时都重置回空列表？我知道我必须有第二组扩展列表，只是不确定如何实现它。