Question

Code Which I have written for this :

   sumBST(BST *root)
     {
         static sum =0;
         if (root!= null)
           {
              if (root->left != null || root->right != null)
                {
                  sum = sum + sumBST(root->left) + sumBST(root->right);
                  return sum;
                }
              else
                {
                   root->data;
                }
           }
         else
            {
               return 0;
            }
        return sum;
     }

I have checked it by drawing recursion tree seems well but Still i am confused at some point I am doing some mistake. Please correct me i am doing something wrong here.

Answer 1

Well, it doesn’t seem like you are actually adding the sum of the leaf nodes.

In parcticular – the line:

root->data

Does not actually return the data, just reads it.
Should be something like that in pseudo code:

sumBST(node):
    if (root == null):
       return 0
    else if (root->left == null && root->right == null)  
       //add the value of the node if it is a leaf, this step is missing
      return root->data;
    else:
      return sumBST(root->left) + sumBST(root->right)

---

EDIT:

The problem in the code are as follows (clarifying and explaining further that point in the answer):

You should return the data of the leaves somewhere – this is not happening anywhere in the code – I suspect you wanted to return it in root->data.

However note that the recursion will go to each and every leaf – it is just missing returning the value from each of them.