二叉树中序遍历

/**创建一个节点
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    
    void midorder(vector&res,TreeNode*root)//传入一个vector容器，接收树中的元素，
    {
        if(root==NULL)
        {
            return ;
        }
        midorder(res,root->left);//按左中右读取
        res.push_back(root->val );//将本节点的元素放到vector容器里
        midorder(res,root->right);
    }
    vector inorderTraversal(TreeNode* root) {
        vectortree;
        midorder(tree,root);
        return tree;
        // write code here
    }
};