题解 | #把二叉树打印成多行#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param pRoot TreeNode类
     * @return int整型ArrayList<ArrayList<>>
     */
    public ArrayList<ArrayList<Integer>> Print (TreeNode pRoot) {
        // write code here
        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
        if (pRoot == null) {
            return list;
        }

        Deque<TreeNode> deque = new LinkedList<TreeNode>();
        deque.offer(pRoot);
        while (!deque.isEmpty()) {
            int count = deque.size();
            ArrayList<Integer> leveList = new ArrayList<Integer>();
            for (int i = 0; i < count; i++) {
                TreeNode node = deque.poll();
                leveList.add(node.val);
                if (node.left != null) {
                    deque.offer(node.left);
                }

                if (node.right != null) {
                    deque.offer(node.right);
                }
            }
            list.add(leveList);
        }
        return list;
    }
}