515. 在每个树行中找最大值

思路：
层次遍历+同深度最大值

# 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 largestValues(self, root: Optional[TreeNode]) -> List[int]:
res = []
if not root:
return res
q = [root]
while q:
tem = []
l = len(q)
for _ in range(l):
node = q.pop(0)
tem.append(node.val)
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
res.append(max(tem))
return res