【递归法】
代码:
import java.util.*; public class Solution { public int[] inorderTraversal (TreeNode root) { List<Integer> list = new ArrayList<Integer>(); inorderTraversal(root,list); int[] arr = new int[list.size()]; for(int i = 0;i < list.size();i++){ arr[i] = list.get(i); } return arr; } public static void inorderTraversal(TreeNode root, List<Integer> list){ if(root == null) {return;} inorderTraversal(root.left,list); list.add(root.val); inorderTraversal(root.right,list); } }