Binary Tree Right Side View

Given a binary tree, imagine yourself standing on therightside of it, return the values of the nodes you can see ordered from top to bottom.

For example: Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

You should return

[1, 3, 4]

.Solution:

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def rightSideView(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root == None:
            return []
        queue = collections.deque([root])
        result = []

        while queue:
            n = len(queue)
            for i in range(n):
                node = queue.popleft()
                if(i == n - 1):
                    result.append(node.val)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
        return result