# 0637. Average of Levels in Binary Tree
###### tags: `Leetcode` `BFS` `Easy` `Level Order Traversal`
Link: https://leetcode.com/problems/average-of-levels-in-binary-tree/
## 思路
层序遍历
注意overflow
## Code

class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        List<Double> ans = new ArrayList<>();
        while(!q.isEmpty()){
            long sum = 0;
            long size = q.size();
            for(int i=0; i<size; i++){
                TreeNode curr = q.poll();
                if(curr.left!=null) q.add(curr.left);
                if(curr.right!=null) q.add(curr.right);
                sum += curr.val;
            }
            ans.add(sum*1.0/size);
        }
        return ans;
    }
}