15 Nov Count Complete Tree Nodes

class Solution {
public:
    
    int helper (TreeNode *root){        
        if (root == NULL)
            return 0;
        
        int no_of_left_nodes = helper (root -> left);
        int no_of_right_nodes = helper (root -> right);
        
        return 1 + no_of_left_nodes + no_of_right_nodes;
    }
    int countNodes(TreeNode* root) {
        return helper (root);
    }
};