Two elements of a binary search tree (BST) are swapped by mistake.

Recover the tree without changing its structure.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution 
{
public:
    void recoverTree(TreeNode *root) 
	{   
		if(root == NULL)
			return;
        vector
  
    res;
		pre_search(root,res);
		if(res.size() == 1)
			return;
		bool flag = false;
		vector
   
     temp; for(int i=1; i
    
     val <= res[i-1]->val) { if(flag == false) { temp.push_back(i-1); flag = true; } else { temp.push_back(i); flag = false; } } } int n = temp.size(); if(n == 1) { int pre = temp[0]; int t = res[pre]->val; res[pre]->val = res[pre+1]->val; res[pre+1]->val = t; } else { int pre = temp[0]; int end = temp[1]; int t = res[pre]->val; res[pre]->val = res[end]->val; res[end]->val = t; } return ; } void pre_search(TreeNode* root, vector
     
      & res) { if(root == NULL) return; pre_search(root->left,res); res.push_back(root); pre_search(root->right,res); } };