算法题：把二叉树打印成多行

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从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/

public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> list = new ArrayList();
        if(pRoot == null) return list;
        ArrayList<TreeNode> subList = new ArrayList();
        subList.add(pRoot);
        //创建每层的容器
        list.add(new ArrayList());
        //换层标记
        subList.add(null);
        while(subList.size() != 0) {
            TreeNode root = subList.remove(0);
            if(root != null) {
                if(root.left != null) {
                   subList.add(root.left); 
                }
                if(root.right != null) {
                    subList.add(root.right);
                }
            }else {
                if(subList.size() != 0) {
                  list.add(new ArrayList());
                  subList.add(null);
                }
                continue;
            }
            list.get(list.size() - 1).add(root.val); 
        }
        return list;
    }
    
}