def invert_tree(self, root: TreeNode) -> TreeNode:
'''
翻转二叉树
Args:
root: 根节点
Returns:
TreeNode
'''
if root == None:
return None
left = self.invert_tree(root.left)
right = self.invert_tree(root.right)
root.left = right
root.right = left
return root
def flatten_for_list(self, root: TreeNode, current_node) -> TreeNode:
'''
循环递归树
Args:
root: 根节点
current_node: 当前节点
Returns:
root
'''
if not root:
return current_node
current_node = self.flatten_for_list(root.right, current_node)
current_node = self.flatten_for_list(root.left, current_node)
root.left = None
root.right = current_node
return root
def merge_trees(t1: TreeNode, t2: TreeNode) -> TreeNode:
'''
合并两棵二叉树
Args:
t1: 二叉树t1
t2: 二叉树t2
Returns:
合并后的二叉树
'''
if t1 == None:
return t2
if t2 == None:
return t1
t1.val += t2.val
t1.left = merge_trees(t1.left, t2.left)
t1.right = merge_trees(t1.right, t2.right)
return t1
Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.
"""
from tree.tree_node import TreeNode
def invert_binary_tree(root: TreeNode):
if not root:
return None
stack = [root] # stack存放还没有做对换的节点
while stack:
node = stack.pop()
if not node:
continue
node.left, node.right = node.right, node.left
stack.append(node.left)
stack.append(node.right)
return root
t = TreeNode(4)
t.left = TreeNode(2)
t.left.left = TreeNode(1)
t.left.right = TreeNode(3)
t.right = TreeNode(7)
t.right.left = TreeNode(6)
t.right.right = TreeNode(9)
print(invert_binary_tree(t))
def max_depth(root: TreeNode):
if not root: return 0
q = [root]
step = 1
all_step = []
while q:
n = len(q)
for _ in range(n):
node = q.pop(0)
if not node:
continue
if not node.left and not node.right:
all_step.append(step)
q.append(node.left)
q.append(node.right)
step += 1
return max(all_step)
t = TreeNode(3)
t.left = TreeNode(9)
t.right = TreeNode(20)
t.right.left = TreeNode(15)
t.right.right = TreeNode(7)
print(min_depth(t))
print(max_depth(t))
self.in_order(root.left)
if self.pre and self.pre.val > root.val:
if not self.first: self.first = self.pre
self.second = root
self.pre = root
self.in_order(root.right)
def recover_tree(self, root: TreeNode):
self.in_order(root)
self.first.val, self.second.val = self.second.val, self.first.val
r = TreeNode(3)
r.left = TreeNode(1)
r.right = TreeNode(4)
r.right.left = TreeNode(2)
recover = RecoverTree()
recover.recover_tree(r)