剑指offer-二叉树按之字形打印

import java.util.ArrayList;
import java.util.Queue;
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 pRoot) {
        //用一个标志位标记是否反转打印
        ArrayList<ArrayList<Integer> > res = new ArrayList<>();
        //先建一个队列
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(pRoot);
        boolean reserve = false;
        while(!queue.isEmpty()){
            int size = queue.size();
            ArrayList<Integer> innerList = new ArrayList<>();
           for(int i = 0; i < size; i++){
               TreeNode node = queue.poll();
               if(node== null){
                   continue;
               }
               //判断插入的顺序
               if(!reserve){
                  innerList.add(node.val);
               }else{
                   innerList.add(0,node.val);
               }
　　　　　　　　　//按照正常的中序遍历，先左后右
               queue.offer(node.left);
               queue.offer(node.right);
            }
            if(innerList.size()>0){
                res.add(innerList);
            }
            //每内循环一次，就翻转一次标志位
            reserve = !reserve;
            
        }
        return res;
    }

}