inorder

class Solution {
public:
    void inorder(TreeNode * root, vector<int> &ans){
        if(root==NULL)return;

        inorder(root->left,ans);
        ans.push_back(root->val);
        inorder(root->right,ans);

        return;

    }
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> ans;
        inorder(root, ans);

        return ans;
    }
};