solution.py

# 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 averageOfLevels(self, root):
        """
        :type root: TreeNode
        :rtype: List[float]
        """
        if not root:
            return []
        res = []
        level = [root]
        while len(level) > 0:
            res.append(sum([x.val for x in level]) / (len(level) * 1.0))
            temp = []
            for node in level:
                if node.left:
                    temp.append(node.left)
                if node.right:
                    temp.append(node.right)
            level = temp
        return res