1. # Definition for a binary tree node.
    2. # class TreeNode:
    3. #     def __init__(self, val=0, left=None, right=None):
    4. #         self.val = val
    5. #         self.left = left
    6. #         self.right = right
    7. class Solution:
    8.     def deepestLeavesSum(self, root: TreeNode) -> int:
    9.         if root == None:
    10.             return None
    11.         queue = [root]
    12.         while queue:
    13.             size = len(queue)
    14.             level = []
    15.             for i in range(size):
    16.                 node = queue.pop(0)
    17.                 level.append(node.val)
    18.                 if node.left:
    19.                     queue.append(node.left)
    20.                 if node.right:
    21.                     queue.append(node.right)
    22.         return sum(level)