题解 | #实现二叉树先序，中序和后序遍历#

import java.util.*;

/*

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

/*

• 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) { List list1=new ArrayList<>(); List list2=new ArrayList<>(); List list3=new ArrayList<>(); preOrder(root,list1); inOrder(root,list2); postOrder(root,list3); int[][] array=new int[3][list1.size()]; for(int a=0;a<list1.size();a++){ array[0][a]=list1.get(a); array[1][a]=list2.get(a); array[2][a]=list3.get(a); } return array;

    // write code here }

  public void preOrder(TreeNode root,List list){ if(root==null){ return; } list.add(root.val); preOrder(root.left,list); preOrder(root.right,list);

  } public void inOrder(TreeNode root,List list){ if(root==null){ return; } inOrder(root.left,list); list.add(root.val); inOrder(root.right,list);

  } public void postOrder(TreeNode root,List list){ if(root==null){ return; }

   postOrder(root.left,list);
   postOrder(root.right,list);
   list.add(root.val);
  

  } }