def removeLeafNodes(self, root: TreeNode, target: int) -> TreeNode:
if not root:
return None
root.left = self.removeLeafNodes(root.left, target)
root.right = self.removeLeafNodes(root.right, target)
if not root.left and not root.right and root.val == target:
return None
else:
return root
def flatten(self, root: TreeNode) -> None:
"""
Do not return anything, modify root in-place instead.
"""
if not root:
return None
self.flatten(root.right)
self.flatten(root.left)
root.right = self.pre
root.left = None
self.pre = root
def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
if not postorder:
return None
# 从后续遍历中获取根节点
v = postorder[-1]
# 从中序遍历中获取左右子树的分割点
n = inorder.index(v)
# 创建根节点
root = TreeNode(v)
# 根据n来构建二叉树进行分割递归
root.left = self.buildTree(inorder[:n], postorder[:n])
root.right = self.buildTree(inorder[n + 1:], postorder[n:-1])
return root
def increasingBST(self, root: TreeNode) -> TreeNode:
res = []
def helper(root: TreeNode) -> List[int]:
if not root:
return
helper(root.left)
res.append(root.val)
helper(root.right)
return res
helper(root)
current = TreeNode(res[0])
root = current
for index, value in enumerate(res):
if index + 1 >= len(res):
break
current.right = TreeNode(res[index + 1])
current = current.right
return root