把二叉树打印成多行

ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> lists = new ArrayList<ArrayList<Integer>>();
if (pRoot == null) {
return lists;
}
Deque<TreeNode> deque = new ArrayDeque<TreeNode>();
deque.push(pRoot);
while (!deque.isEmpty()) {
int low = 0;
int layerNum = deque.size();
ArrayList<Integer> list = new ArrayList<Integer>();
// 根据low、layerNum变量就可以知道每层的节点个数
while (low++ < layerNum) {
TreeNode temp = deque.pop();
list.add(temp.val);
if (temp.left != null) {
deque.offer(temp.left); // 注意不是push()
}
if (temp.right != null) {
deque.offer(temp.right);
}
}
lists.add(list);
}
return lists;

}