剑指 Offer 32 - II. 从上到下打印二叉树 II

剑指 Offer 32 - II. 从上到下打印二叉树 II

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> res = new ArrayList<>();
        if(root == null) return res;
        Deque<TreeNode> queue = new ArrayDeque<>();
        queue.offer(root);

        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> tmp = new ArrayList<>();
            for(int i = 0; i < size; i++){
                TreeNode cur = queue.poll();
                tmp.add(cur.val);
                if(cur.left != null) queue.offer(cur.left);
                if(cur.right != null) queue.offer(cur.right);
            }
            res.add(tmp);
        }

        return res;
    }
}