力扣——二叉树的层平均值

/**
 * 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> doubles = new ArrayList<>();
        if (root == null) return doubles;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            double ave = 0;
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                if (node.left != null) queue.add(node.left);
                if (node.right != null) queue.add(node.right);
                ave += node.val;
            }
            ave = ave * 1.0d / size;
            doubles.add(ave);
        }
        return doubles;
    }

}