/**

* Definition for binary tree

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

public class FixBST {

TreeNode n1, n2, prevNode;

public void recoverTree(TreeNode root) {

prevNode = null;

n1 = null; n2 = null;

inorder(root);

int tmp = n1.val;

n1.val = n2.val;

n2.val = tmp;

}

void inorder(TreeNode root){

if(root == null) return;

inorder(root.left);

if(prevNode != null && prevNode.val > root.val){

n2 = root;

if(n1 == null)

n1 = prevNode;

}

prevNode = root;

inorder(root.right);

}

}