按之字形顺序打印二叉树

import java.util.ArrayList;
import java.util.LinkedList;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode root) {
        ArrayList<ArrayList<Integer>> res=new ArrayList<ArrayList<Integer>>();
        if(root==null){
            return res;
        }
        ArrayList<Integer> list=new ArrayList<Integer>();
        LinkedList<TreeNode> que=new LinkedList<TreeNode>();
        que.offer(root);
        int curNode=1;
        boolean leftToRight=true;
        while(!que.isEmpty()){
            root=que.poll();
            --curNode;
            if(root.left!=null){
                que.offer(root.left);
            }
            if(root.right!=null){
                que.offer(root.right);
            }
            list.add(root.val);
            if(curNode==0){
                curNode=que.size();
                if(leftToRight){
                    res.add(list);
                }else{
                    res.add(reverseList(list));
                }
                leftToRight=!leftToRight;
                list=new ArrayList<Integer>();
            }
        }
        return res;
    }
    private ArrayList<Integer> reverseList(ArrayList<Integer> list){
        int len=list.size();
        ArrayList<Integer> res=new ArrayList<Integer>();
        for(int i=len-1;i>=0;--i){
            res.add(list.get(i));
        }
        return res;
    }
}