// @Title: 二叉树的中序遍历 (Binary Tree Inorder Traversal)
// @Author: qisiii
// @Date: 2022-03-01 21:20:28
// @Runtime: 0 ms
// @Memory: 39.6 MB
// @comment: 
// @flag: 
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        if(root==null){
            return new ArrayList();
        }
        List<Integer> zhong=new ArrayList();
        zhong.addAll(inorderTraversal(root.left));
        zhong.add(root.val);
        zhong.addAll(inorderTraversal(root.right));
        return zhong;
    }
}

// @Title: 二叉树的中序遍历 (Binary Tree Inorder Traversal)
// @Author: qisiii
// @Date: 2024-09-14 21:05:57
// @Runtime: 0 ms
// @Memory: 40.7 MB
// @comment: 
// @flag: 
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
     List<Integer> result=new ArrayList<>();
        sort(result,root);
        return result;
    }
    private void sort(List<Integer> result,TreeNode node){
        if(node!=null){
            sort(result,node.left);
            result.add(node.val);
            sort(result,node.right);
        }
    }
}