2025-08-01 12:50:58 +0000 UTC

# 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 increasingBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if root is None:
            return None
        def dfs(node: TreeNode) -> tuple[TreeNode, TreeNode]:
            if node.left:
                root, tail = dfs(node.left)
                tail.right = node
                tail = node
                node.left = None
            else:
                root, tail = node, node
            if node.right:
                right_root, right_tail = dfs(node.right)
                tail.right = right_root
                tail = right_tail
            return root, tail

        root, tail = dfs(root)
        return root