/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

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

* }

*/

class Solution {

public List<Integer> rightSideView(TreeNode root) {

if(root == null) return Collections.emptyList();

TreeNode dummy = new TreeNode(0);

Queue<TreeNode> p = new ArrayDeque<>();

p.offer(root);

p.offer(dummy);

List<Integer> result = new ArrayList<>();

int right = 0;

while(!p.isEmpty()) {

TreeNode t = p.poll();

if(t != dummy) {

right = t.val;

if(t.left != null) p.offer(t.left);

if(t.right != null) p.offer(t.right);

}else {

if(!p.isEmpty()) p.offer(dummy);

result.add(right);

}

}

return result;

}

}