solved 'Binary Tree Right Side View' on LeetCode https://leetcode.com/problems/binary-tree-right-side-view/

btree_rightmost.py

# 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 not root:
      return []
        
    q, right_side = collections.deque([root]), []
    rightmost_node = root
    
    while q:
      top_node = q.popleft()
      if top_node.left:
        q.append(top_node.left)
      if top_node.right:
        q.append(top_node.right)
      
      if top_node == rightmost_node:
        right_side.append(top_node.val)
        rightmost_node = q[-1] if q else None
        
    return right_side