[Leetcode] Binary tree-- 637. Average of Levels in Binary Tree

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

Input:
    3
   / 
  9  20
    /  
   15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 1


Solution:

   # it actually examines the knowledge of level order
   #refer to the similar problem : 102. Binary Tree Level Order Traversal

        if not root:
            return []
        d = collections.deque()
        d.append(root)
        resLst = []
        while(len(d)):
            n = len(d)
            lst = []
            tmpSum = 0.0
            count = n
            while(n > 0):
                node = d.popleft()
                tmpSum += node.val
                if node.left:
                    d.append(node.left)
                if node.right:
                    d.append(node.right)
                n -= 1
            resLst.append(tmpSum/count)

        return resLst