Alternate C++ solution #98. Validate Binary Search Tree about leetcode HOT 4 CLOSED

 class Solution
 {
    vector<int> res;
    bool inorderTraversal(TreeNode *root)
    {
        if (root == NULL)
            return true;
        bool r1, r2;
        if (root->left != NULL && root->left->val >= root->val)
            return false;
        else
            r1 = inorderTraversal(root->left);
        res.push_back(root->val);
        if (root->right != NULL && root->right->val <= root->val)
            return false;
        else
            r2 = inorderTraversal(root->right);
        return r1 && r2;
    }

    public:
        bool isValidBST(TreeNode *root)
        {
            if (!inorderTraversal(root))
                return false;
            for (int i = 1; i < res.size(); i++)
            {

                if (res[i] <= res[i - 1])
                    return false;
            }
            return true;
        }
};