#include <bits/stdc++.h>
using namespace std;
struct TreeNode
{
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode() : val(0), left(nullptr), right(nullptr) {}
	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
	TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};
class Solution
{
public:
	void recoverTree(TreeNode *root)
	{
		dfs(root);
		int tmp = p0_->val;
		p0_->val = p1_->val;
		p1_->val = tmp;
	}
private:
	int wrong_ = 0;
	TreeNode *prev_ = nullptr;
	TreeNode *p0_ = nullptr;
	TreeNode *p1_ = nullptr;
	void dfs(TreeNode *root)
	{
		if (root == nullptr || wrong_ == 2)
		{
			return;
		}
		dfs(root->left);
		if (prev_ != nullptr && prev_->val > root->val)
		{
			if (++wrong_ == 1)
			{
				p0_ = prev_;
				p1_ = root;
			}
			else if (wrong_ == 2)
			{
				p1_ = root;
			}
		}
		prev_ = root;
		dfs(root->right);
	}
};