text: 
  /**
   * Definition for a binary tree node.
   * struct TreeNode {
   *     int val;
   *     TreeNode *left;
   *     TreeNode *right;
   *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
   * };
   */
  class Solution {
  public:
          int res=0;
      int countNodes(TreeNode* root) {
            if(root==NULL)
                    return 0;
              res++;
              countNodes(root->left);
              countNodes(root->right);
            
              
            return res;                  
      }
  };
  