代码随想录算法训练营第二十一天| 669. 修剪二叉搜索树|108.将有序数组转换为二叉搜索树|538.把二叉搜索树转换为累加树

669. 修剪二叉搜索树

# Definition for a binary tree node.

# class TreeNode:

# def __init__(self, val=0, left=None, right=None):

# self.val = val

# self.left = left

# self.right = right

class Solution:

    def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]:

        if not root:

            return None

        if root.val>high:

            return self.trimBST(root.left,low,high)

        if root.val<low:

            return self.trimBST(root.right,low,high)

        root.left=self.trimBST(root.left,low,high)

        root.right=self.trimBST(root.right,low,high)

        return root

108.将有序数组转换为二叉搜索树

# Definition for a binary tree node.

# class TreeNode:

# def __init__(self, val=0, left=None, right=None):

# self.val = val

# self.left = left

# self.right = right

class Solution:

    def sortedArrayToBST(self, nums: List[int]) -> Optional[TreeNode]:

        if not nums:

            return 

        root=TreeNode(nums[len(nums)//2])

        root.left=self.sortedArrayToBST(nums[:len(nums)//2])

        root.right=self.sortedArrayToBST(nums[len(nums)//2+1:])

        return root

538.把二叉搜索树转换为累加树 

# Definition for a binary tree node.

# class TreeNode:

# def __init__(self, val=0, left=None, right=None):

# self.val = val

# self.left = left

# self.right = right

class Solution:

    def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:

        self.pre=0

        return self.sumbst(root)

    def sumbst(self,root):

        if not root:

            return None

        self.sumbst(root.right)

        root.val+=self.pre

        self.pre=root.val

        self.sumbst(root.left)

        return root