Calculate the number of element of Non-Binary Tree

Question

I have made a function to calculate the number of element(nodes) of Non-Binary Tree, but it always return the correct answer - 1 (eg if the number of element is 10 it returns 9) like I am missing calculting the root. I spent hours trying to fix it and it did not work!

Here is the part of my code where I build the tree:

NaryTreeNode<Integer> iRoot = new NaryTreeNode<Integer>(25);
NaryTreeNode<Integer> i1 = new NaryTreeNode<Integer>(11);
NaryTreeNode<Integer> i2 = new NaryTreeNode<Integer>(-23);
NaryTreeNode<Integer> i3 = new NaryTreeNode<Integer>(67);
NaryTreeNode<Integer> i4 = new NaryTreeNode<Integer>(-7);
NaryTreeNode<Integer> i5 = new NaryTreeNode<Integer>(88);
NaryTreeNode<Integer> i6 = new NaryTreeNode<Integer>(47);
NaryTreeNode<Integer> i7 = new NaryTreeNode<Integer>(91);
NaryTreeNode<Integer> i8 = new NaryTreeNode<Integer>(-34);
NaryTreeNode<Integer> i9 = new NaryTreeNode<Integer>(15);

iRoot.addChild(i1);
iRoot.addChild(i2);
iRoot.addChild(i3);

i1.addChild(i4);
i1.addChild(i5);

i2.addChild(i6);

i4.addChild(i7);
i4.addChild(i8);
i4.addChild(i9);

LinkedNaryTree<Integer> iTree = new LinkedNaryTree<Integer>(iRoot);

System.out.println(iTree.size(iTree.getRoot()));

Here is the code of my method:

public int size(NaryTreeNode<T> node) {
        if (node == null)
            return 0;

        int counter = 0;
        for (int i = 0; i < node.getNumChildren(); i++) {
            counter += 1 + size(node.getChild(i));
        }

        return counter;
    }

Answer 1

The reason you get 1 less is that you account for a node outside of the function call ( 1 + size() ), yet a call to size should include in its count the node you pass as argument.

So there are two places where you need a fix:

• int counter = 0; should be int counter = 1; so to account for node , which we already know at that point is not null.

• counter += 1 + size(node.getChild(i)); on the other hand is counting 1 too many. Here I think you intended with that 1 + to account for the child, but size() should include in its returned count the child itself (done by the fix above). So this should just be:

   counter += size(node.getChild(i));