637_二叉树的层平均值

描述

给定一个非空二叉树的根节点 root , 以数组的形式返回每一层节点的平均值。与实际答案相差 10-5 以内的答案可以被接受

思路

无需思路，乱杀

解答

# 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]:
        if root is None:
            return []
        all_level = [root, ]
        ret = []
        while all_level:
            level_cnt = 0
            level_total = 0
            nxt_level = []
            for node in all_level:
                if node:
                    level_cnt+=1
                    level_total+=node.val
                    node.left and nxt_level.append(node.left) or None
                    node.right and nxt_level.append(node.right) or None
            if level_cnt > 0:
                ret.append(level_total/level_cnt)
            else:
                ret.append(None)
            all_level = nxt_level
        return ret