在leetcode 如下题目中使用队列
637. 二叉树的层平均值:
# 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 = rightclass Solution:def averageOfLevels(self, root: Optional[TreeNode]) -> List[float]:ans = []queue = deque([root])while queue:sum = 0cnt = len(queue)for i in range(cnt):node = queue.popleft()sum += node.valif node.left:queue.append(node.left)if node.right:queue.append(node.right)ans.append(sum/cnt)return ans