二叉树的层平均值

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LeetCode 637

https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/

代码如下

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> res = new ArrayList<>();
        if (root == null) {
            return res;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (queue.size() != 0) {
            int len = queue.size();
            double curSum = 0;
            for (int i = 0; i < len; i++) {
                TreeNode curNode = queue.poll();
                curSum += curNode.val;
                if (curNode.left != null) {
                    queue.add(curNode.left);
                }
                if (curNode.right != null) {
                    queue.add(curNode.right);
                }
            }
            res.add(curSum / len);
        }
        return res;
    }
}