def kth_node_in_BST(root, k):
"""
:param root: Binary Search Tree root
:param k: kth smallest
:return: kth smallest node
"""
def recursion(root, k):
nonlocal target
if not root:
return k
k = recursion(root.left, k)
if not target:
if k == 1:
target = root
else:
k -= 1
if not target:
k = recursion(root.right, k)
return k
target = None
recursion(root, k)
return target
from datstru import list_to_treenode
tree = list_to_treenode([8, 6, 10, 5, 7, 9, 11])
k = 1
ans = kth_node_in_BST(tree, k)
print()
1
3 2
4 5 6 7
15 14 13 12 11 10 9 8
"""
def print_tree_lines(root):
"""
:param root: tree root
:return: None
"""
layer = [root]
next_layer = []
reverse = -1
while layer:
for node in layer[::-1]:
if node:
print(node.val, end=" ")
next_layer.extend([node.left, node.right][::-reverse])
print()
layer = next_layer
next_layer = []
reverse = -reverse
return
from datstru import list_to_treenode
root = list_to_treenode(list(range(1, 32)))
print_tree_lines(root)
面试题55:二叉树的深度
题目1：二叉树的深度
输入一棵二叉树的根节点，求该树的深度。从根节点到叶节点一次经过的节点
形成树的一条路径，从最长路径的长度为树的深度。
例：
1
/ \
2 3
/ \ \
4 5 6
/
7
深度为4。
"""
def depth_of_tree(root):
"""
:param root: tree root
:return: height of tree
"""
if not root:
return 0
left = depth_of_tree(root.left)
right = depth_of_tree(root.right)
return max(left, right) + 1
from datstru import list_to_treenode
tree = list_to_treenode([1,2,3,4,5,'null',6,'null','null',7])
print(depth_of_tree(tree))
return seq
seq = []
preorder(root)
return seq
def deserialize(sequence):
"""
:param sequence:pre-order val list
:return: tree root
"""
def rebuild(seqence, i):
val = seqence[i]
if val == '$':
return None
root = TreeNode(val)
root.left = rebuild(seqence, i + 1)
root.right = rebuild(seqence, i + 2)
return root
if not sequence:
return None
return rebuild(sequence, 0)
root = list_to_treenode([1, 2, 3, 4, 'null', 5, 6])
seq = serialize(root)
tree = deserialize(seq)
print(seq)