Problem URL: Average of levels in binary tree

We will run BFS and after traversal of each level, we append the average in our result, and finally return it after the end of traversal.

# 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 averageOfLevels(self, root: Optional[TreeNode]) -> List[float]:
        q = collections.deque([root])
        res = []
        while q:
            level = []
            qLen = len(q)
            for i in range(qLen):
                node = q.pop()
                level.append(node.val)

                if node.left: q.appendleft(node.left)
                if node.right: q.appendleft(node.right)
            res.append(mean(level))
        return res

Time Complexity: O(n)
Space Complexity: O(n)