/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List rightSideView(TreeNode root) {
List result = new ArrayList();
if (root == null) return result;
Queue queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
int size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode node = queue.remove();
if (i == 0) result.add(node.val);
if (node.right != null) {
queue.add(node.right);
}
if (node.left != null) {
queue.add(node.left);
}
}
}
return result;
}
}