Question

This may be a simple fix – but I’m trying to sum together all the nodes (Size property from the Node class) on the binary search tree. Below in my BST class I have the following so far, but it returns 0:

    private long sum(Node<T> thisNode)     {         if (thisNode.Left == null && thisNode.Right == null)             return 0;         if (node.Right == null)             return sum(thisNode.Left);         if (node.Left == null)              return sum(thisNode.Right);           return sum(thisNode.Left) + sum(thisNode.Right);     } 

Within my Node class I have Data which stores Size and Name in their given properties. I’m just trying to sum the entire size. Any suggestions or ideas?

Answer 1

It’s because you’re returning zero when you reach a leaf node. You should be returning the size stored in that leaf node.

In addition, if your non-leaf nodes also have a size, you’ll need to process them as well thus:

private long sum(Node<T> thisNode) {     if (thisNode.Left == null && thisNode.Right == null)         return thisNode.Size;     if (node.Right == null)         return thisNode.Size + sum(thisNode.Left);     if (node.Left == null)          return thisNode.Size + sum(thisNode.Right);     return thisNode.Size + sum(thisNode.Left) + sum(thisNode.Right); } 

If your non-leaf nodes don’t have size, use:

private long sum(Node<T> thisNode) {     if (thisNode.Left == null && thisNode.Right == null)         return thisNode.Size;     if (node.Right == null)         return sum(thisNode.Left);     if (node.Left == null)          return sum(thisNode.Right);     return sum(thisNode.Left) + sum(thisNode.Right); } 

A more elegant version of the first one is:

private long sum(Node<T> thisNode) {     if (thisNode == null)         return 0;     return thisNode.Size + sum(thisNode.Left) + sum(thisNode.Right); }