二叉树669|108|538

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
        if root.val < low:
            return self.trimBST(root.right, low, high)
        elif root.val > high:
            return self.trimBST(root.left, 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]:
        left = 0
        right = len(nums) - 1
        return self.traversal(nums, left, right)

    def traversal(self, nums, left, right):
        if left > right:
            return
        mid = (right - left) // 2 + left
        node = TreeNode(nums[mid])
        node.left = self.traversal(nums, left, mid - 1)
        node.right = self.traversal(nums, mid + 1, right)
        return node

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 __init__(self):
        self.pre = 0
    def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        return self.traversal(root)
    def traversal(self, node) -> int:
        if not node:
            return
        self.traversal(node.right)
        node.val += self.pre
        self.pre = node.val
        self.traversal(node.left)
        return node