/**

* Definition for binary tree

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

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

* }

*/

public class FlatterBT {

public void flatten(TreeNode root) {

helper(root);

}

TreeNode helper(TreeNode curr){

if(curr == null)

return null;

TreeNode tail1 = helper(curr.left);

TreeNode tail2 = helper(curr.right);

TreeNode temp = curr.right;

curr.right = curr.left;

curr.left = null;

tail1 = tail1==null? curr : tail1;

tail1.right = temp;

return tail2==null? tail1 : tail2;

}

/*

public void flatten(TreeNode root) {

if(root == null) return;

TreeNode right = root.right;

root.right = root.left;

root.left = null;

TreeNode ptr = root;

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

ptr.right = right;

flatten(root.right);

}

*/

}