题解 | #删除链表的节点#

利用递归进行先序，中序，后序排列，利用list列表存放排序后的数据 排序结束后遍历列表，存入数组中

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型二维数组
     */
    public int[][] threeOrders (TreeNode root) {
        // write code here
        List<Integer> list1=new ArrayList<>();
         List<Integer> list2=new ArrayList<>();
         List<Integer> list3=new ArrayList<>();
        preOrder(root,list1);
         inOrder(root,list2);
         postOrder(root,list3);
        
        int[][] res=new int[3][list1.size()];
        for(int i=0;i<list1.size();i++){
            res[0][i]=list1.get(i);
            res[1][i]=list2.get(i);
            res[2][i]=list3.get(i);
        }
       return res;
        
    }
    //先序
    public void preOrder(TreeNode root,List<Integer> list){//用list列表存放数据
        if(root==null) return;
            list.add(root.val);
            preOrder(root.left,list);
            preOrder(root.right,list);
        
    }
    //中序
    public void inOrder(TreeNode root,List<Integer> list){
        if(root==null) return;
            inOrder(root.left,list);
            list.add(root.val);
            inOrder(root.right,list);
        
    }
    //后序
    //中序
    public void postOrder(TreeNode root,List<Integer> list){
        if(root==null) return;
            postOrder(root.left,list);
            postOrder(root.right,list);
            list.add(root.val);
    }
    
}