# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def deepestLeavesSum(self, root: Optional[TreeNode]) -> int:
if not root:
return 0
levels = []
q = deque([root])
while q:
size = len(q)
curr = []
for _ in range(size):
node = q.popleft()
curr.append(node.val)
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
if levels:
levels.pop()
levels.append(curr)
return sum(levels[-1])
