Average of Levels in Binary Tree

给一个二叉树, 返回每层的均值. 直接层遍历即可.

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