637. Average of Levels in Binary Tree

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class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> resultList = new ArrayList<>();

        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            double sum = 0; // 防止整数越界
            double size = queue.size();
            for (int i = queue.size(); i > 0; i--) {
                TreeNode node = queue.poll();
                sum += node.val;
                if (node.left != null) {
                    queue.offer(node.left);
                }
                if (node.right != null) {
                    queue.offer(node.right);
                }
            }

            resultList.add(sum / size);
        }

        return resultList;
    }
}

注意潜在的整数越界问题。

References

637. Average of Levels in Binary Tree