递归
import java.util.*; /* * public class TreeNode { * int val = 0; * TreeNode left = null; * TreeNode right = null; * public TreeNode(int val) { * this.val = val; * } * } */ public class Solution { public void inorder(ArrayList<Integer> list,TreeNode root){ if(root==null){ return ; } inorder(list,root.left); list.add(root.val); inorder(list,root.right); } /** * 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可 * * * @param root TreeNode类 * @return int整型一维数组 */ public int[] inorderTraversal (TreeNode root) { // write code here ArrayList<Integer> list=new ArrayList<>(); inorder(list,root); int[] res=new int[list.size()]; res=list.stream().mapToInt(Integer::valueOf).toArray();//ArrayList转化为int[] return res; } }