【剑指offer】把二叉树打印成多行

重新建了一个Node数据结构，Node{TreeNode 树节点,level 层次}，进行层次遍历BFS。
书上的用两个变量控制将每层树节点打印到一行，很nice~

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

class Node {
    TreeNode treeNode;
    int level;

    public Node(TreeNode treeNode, int level) {
        this.treeNode = treeNode;
        this.level = level;
    }
}

public class Solution {
    ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        Queue<Node> queue = new LinkedList<>();
        if (pRoot == null) {
            return list;
        }
        queue.add(new Node(pRoot, 1));
        ArrayList<Integer> arraylist = new ArrayList<>();
        int level = 1;
        while (!queue.isEmpty()) {
            Node node = queue.remove();
            if (node.level != level) {
                list.add(arraylist);
                arraylist = new ArrayList<>();
                level++;
            }
            arraylist.add(node.treeNode.val);
            if (node.treeNode.left != null) {
                queue.add(new Node(node.treeNode.left, node.level + 1));
            }
            if (node.treeNode.right != null) {
                queue.add(new Node(node.treeNode.right, node.level + 1));
            }
        }
        list.add(arraylist);
        return list;
    }
}