leecode Binary Tree Level Order Traversal II java

做完这道题，只能说基本功很重要，数组中套数组就不会用了，过几天吧1做了，看自己到底等没。

https://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/

import java.util.*;

/**

 * Definition for binary tree

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

 

public class Solution {

    public List<List<Integer>> levelOrderBottom(TreeNode root) {

       // List<List<Integer>> list=new ArrayList<ArrayList<Integer>>();

          ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();  

          if(root==null) return (List)list;

         

          

       

          

    

        Queue<TreeNode> q=new LinkedList<TreeNode>();

        q.offer(root);

        while(!q.isEmpty())

        {

          ArrayList<Integer> temp=new ArrayList<Integer>();

          int len=q.size();

        

            for(int i=0;i<len;i++)

            {

                TreeNode t=q.poll();

                temp.add(t.val);

                if(t.left!=null) q.offer(t.left);

                

                if(t.right!=null) q.offer(t.right);

            }

            

           

            

             ArrayList<Integer> arry2=new ArrayList<Integer>(temp);

             list.add(arry2);

            temp.clear();

            

        }

        int n=list.size();

        

    for(int i=0;i<n/2;i++)

    {

        ArrayList temp=list.get(i);

        list.set(i,list.get(n-1-i));

        

        list.set(n-i-1,temp);

        //swap  

       

    }

        

   

        

        return (List)list;

    

    

        

    }

}