LeetCode99 恢复二叉搜索树（Morris中序遍历）

LeetCode99 恢复二叉搜索树

Morris中序遍历 + 记录逆序对

Morris遍历

# 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 recoverTree(self, root: Optional[TreeNode]) -> None:
        """
        Do not return anything, modify root in-place instead.
        """
        x, y, pre, cur = None, None, None, None

        while root:
            if root.left:
                cur = root.left
                while cur.right and cur.right != root:
                    cur = cur.right
                if cur.right is None:
                    cur.right, root = root, root.left
                else:
                    if pre and pre.val > root.val:
                        y = root
                        if x is None: x = pre
                    pre, cur.right, root = root, None, root.right
            else:
                if pre and pre.val > root.val:
                    y = root
                    if x is None: x = pre
                pre, root = root, root.right
        
        if x and y: x.val, y.val = y.val, x.val