/**

* Definition for binary tree

* struct TreeNode {

* int val;

* TreeNode *left;

* TreeNode *right;

* TreeNode(int x) : val(x), left(NULL), right(NULL) {}

* };

*/

//reviewed

class Solution {

public:

TreeNode *first;

TreeNode *second;

TreeNode *pre;

void inOrder(TreeNode *root){

if (root==NULL){return;}

else{

inOrder(root->left);

if (pre == NULL){pre = root;}

else {

if (pre->val > root->val){

if (first==NULL) {first = pre;}

second = root;

}

pre = root;

}

inOrder(root->right);

}

}

void recoverTree(TreeNode *root) {

// Start typing your C/C++ solution below

// DO NOT write int main() function

pre = NULL;

first = NULL;

second= NULL;

inOrder(root);

int val;

val = first->val;

first->val=second->val;

second->val=val;

return;

}

};

//revisited.