鉴于这棵树:
7
5 9
_ 6 8 _
_ _ _ _
我希望输出为:
[[Node(7)], [Node(5), Node(9)], [None, Node(6), Node(8), None], [None, None, None, None]]
因此,重要的是包含“无”并且输出是列表中的列表。
我尝试了很多东西,但这就是我现在所处的位置:
class Node(object):
def __init__(self, key, value=None):
self.key = key
self.value = value
self.parent = None
self.left_child = None
self.right_child = None
self.height = 0
def breadth_first_traversal(self):
self.height = 1
to_do = [self.root]
if (self.root == None):
return to_do
output = []
current_height = self.height
output.append([str(node) for node in to_do])
while (to_do):
done = []
current = to_do.pop(0)
if (current.height > current_height):
current_height += 1
if (current.left_child):
current.left_child.height = current_height + 1
to_do.append(current.left_child)
done.append(current.left_child)
elif (not current.left_child):
done.append(None)
if (current.right_child):
current.right_child.height = current_height + 1
to_do.append(current.right_child)
done.append(current.right_child)
elif (not current.right_child):
done.append(None)
output.append([str(node) for node in done])
print(output)
return output
现在的输出是:
[['7'], ['5', '9'], ['None', '6'], ['8', 'None'], ['None', 'None'], ['None', 'None']]
我理解为什么要制作2个元素的列表,因为这就是我现在应该做的。我只是不知道如何考虑水平。
一种可能性是找到所有节点,包括存储None
的叶子,以及每个节点的深度,然后按深度分组:
为简单起见,我创建了一个二叉树,可以使用kwargs
轻松初始化,以及遍历树并提供运行深度值的方法:
from itertools import groupby
class Node:
def __init__(self, **kwargs):
self.__dict__ = {i:kwargs.get(i, None) for i in ['left', 'right', 'value']}
def get_depths(self, _count = 0):
yield [_count, self.value]
if self.left is not None:
yield from self.left.get_depths(_count+1)
else:
yield [_count+1, None]
if self.right is not None:
yield from self.right.get_depths(_count+1)
else:
yield [_count+1, None]
tree = Node(value=7, left=Node(value=5, right=Node(value=6)), right=Node(value=9, left=Node(value=8)))
flattened = [[c for _, c in b] for _, b in groupby(sorted(list(tree.get_depths()), key=lambda x:x[0]), key=lambda x:x[0])]
输出:
[[7], [5, 9], [None, 6, 8, None], [None, None, None, None]]
由于您正在使用二叉搜索树,因此将结果作为元组连接到数组是有意义的。
如果要根据数组的相对深度连接数组,则需要实现一个聚合器函数,该函数继续将元素附加到列表,直到深度递增为止,此时列表将被保存并清除以供下一组使用。
或者,您可以将结果传递给辅助函数,该函数只需按照您希望的方式连接元素。
编辑1:以下应该有效;但是,我还没有测试过。我只是将done
移到while
循环之外,这样它就不会在每次迭代后重新初始化。此外,当深度增加时,我只将done
附加到output
,因为这是没有其他元素要处理的时刻。
class Node(object):
def __init__(self, key, value=None):
self.key = key
self.value = value
self.parent = None
self.left_child = None
self.right_child = None
self.height = 0
def breadth_first_traversal(self):
self.height = 1
to_do = [self.root]
if (self.root == None):
return to_do
output = []
current_height = self.height
output.append([str(node) for node in to_do])
done = []
while (to_do):
current = to_do.pop(0)
if (current.height > current_height):
current_height += 1
output.append([str(node) for node in done])
done = []
if (current.left_child):
current.left_child.height = current_height + 1
to_do.append(current.left_child)
done.append(current.left_child)
elif (not current.left_child):
done.append(None)
if (current.right_child):
current.right_child.height = current_height + 1
to_do.append(current.right_child)
done.append(current.right_child)
elif (not current.right_child):
done.append(None)
print(output)
return output