二叉树的打印

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。

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

 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>> level = new ArrayList<>();
		ArrayList<Integer> arrays = new ArrayList<>();
		LinkedList<TreeNode> queue = new LinkedList<>();
        if (pRoot == null) {
			return level;
		}
		queue.add(pRoot);
		TreeNode current = null;
		TreeNode last = pRoot;//正在打印的当前行的最右节点
		TreeNode nlast = null;//表示下一行的最右节点
		while (queue.size() != 0) {
			current = queue.poll();
			arrays.add(current.val);
			if (current.left != null) {
				queue.add(current.left);
				nlast = current.left;
			}
			if (current.right != null) {
				queue.add(current.right);
				nlast = current.right;
			}
			if (current == last) {
				level.add(arrays);
				arrays = new ArrayList<>();
				last = nlast;
			}

		}
		return level;

    }

}