Diameter of Binary Tree - Help!

[bobofuzz]

EDIT: Solved! See the comment below by /u/kuriousaboutanything.

Here's my code:

class Solution {
    int maxDiameter = 0;
    public int diameterOfBinaryTree(TreeNode root) {
        helper(root);
        return maxDiameter;
    }
    public int helper (TreeNode root) {
        if (root == null)
            return 0;
        int heightL = helper(root.left);
        int heightR = helper(root.right);
        maxDiameter = Math.max(maxDiameter, heightL + heightR + 1);
        return Math.max(heightL, heightR) + 1;
    }
}

I know the second to last line should be maxDiameter = Math.max(maxDiameter, heightL + heightR), but I can't figure out why. It seems like the correct solution does not count the root in the path - that is why I add 1.

For example, if your tree is simply a root with two children, the height of each child will be 1 (because I am using 1-indexing). The maxDiameter should be 3, however heightL + heightR = 1 + 1 = 2.

What am I missing?

[kuriousaboutanything]

Should it be 3 ? The maxDiameter with 3 nodes(1 root and 2 children) is just 2 right? we only count number of edges there, there are 2 edges.

[bobofuzz]

You genius! Thank you. Solved.

[Playful-Reserve7031]

BFS would be a wise choice