算法题：二叉树层序遍历，进一步提问：要求每层打印出一个换行符？

Answer 1

考察点：二叉树

 

public
List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> res =new ArrayList<List<Integer>>();
        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
        if (root == null) {
            return res;
        }
        queue.offer(root);
        while (queue.size() != 0) {
            List<Integer> l = new ArrayList<Integer>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode temp = queue.poll();
                l.add(temp.val);
                if (temp.left != null) {
                    queue.offer(temp.left);
                }
                if (temp.right != null) {
                    queue.offer(temp.right);
                }
            }
            res.add(l);
        }
        return res;
}