按之字形打印二叉树！！！

Posted 2023-02-18 Putarmor

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;

    


*/
//8.13 被汤老师灵魂拷问时刻 出了这道题
public class Solution 
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) 
        
        ArrayList<ArrayList<Integer>> list1 = new ArrayList<>();
        if(pRoot == null)
            return list1;
        
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(pRoot);
        boolean flag = false; //打印标志位，比如第一张从左往右，第二行从右往左
        while(!queue.isEmpty())
            ArrayList<Integer> list2 = new ArrayList<>();
            int size = queue.size(); //得到队列的大小
            for(int i = 0; i < size; i++)
                TreeNode cur = queue.poll();
                
                //下面对标志位判断
                //当标志位为false时从左向右打，标志位为true时从右向左打
                if(!flag)
                   list2.add(cur.val); 
                else
                    list2.add(0,cur.val);
                
                
                if(cur.left != null)
                    queue.offer(cur.left);
                
                if(cur.right != null)
                    queue.offer(cur.right);
                
            
            //每一行打印结束后将其加入到外部list1中
            list1.add(list2);
            //每打印一行，改变一次标志位
            flag = !flag;
        
        return list1;