/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

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

* }

*/

// This solution needs to traverse the left subtree everytime we need to combine the result.

// So it might get slow

class Solution {

public TreeNode increasingBST(TreeNode root) {

if(root == null) return root;

if(root.left == null && root.right == null) return root;

if(root.right != null) root.right = increasingBST(root.right);

if(root.left != null) {

TreeNode left = increasingBST(root.left);

TreeNode p = left;

while(p.right != null) p = p.right;

p.right = root;

return left;

} else {

return root;

}

}

}

// In order traverse solution

class Solution {

private final TreeNode dummy = new TreeNode(0);

private TreeNode p = dummy;

public TreeNode increasingBST(TreeNode root) {

inorder(root);

return dummy.right;

}

private void inorder(TreeNode root) {

if(root == null) return;

inorder(root.left);

p.right = root;

root.left = null;

p = p.right;

inorder(root.right);

}

}