```
# 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 largestValues(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root:
return []
queue = [root]
length = len(queue)
ans = []
while length:
# put question specific code here for BFS problems
# get the average of the current level
max_val = max([node.val for node in queue])
ans.append(max_val)
# enqueue the children of the all nodes
# in the current level
tmpq = []
for node in queue:
if node.left:
tmpq.append(node.left)
if node.right:
tmpq.append(node.right)
# reassign the queue
queue = tmpq
length = len(queue)
return ans
```