Diameter of Binary Tree - Better Design

Question

I have written a code for finding diameter of Binary Tree. Need suggestions for the following:

1. Can I do this without using static variable at class level?

Answer 1

Here is a solution in Java that has O(N) time complexity. It calculates the height in the same recursion when calculating the diameter. Reference Link

private class HeightWrapper {
    int height = 0;
}

private int getDiameter_helper(BinaryTreeNode root, HeightWrapper wrapper) {
    if (root == null) {
        return 0; // diameter and height are 0
    }

    /* wrappers for heights of the left and right subtrees */
    HeightWrapper lhWrapper = new HeightWrapper();
    HeightWrapper rhWrapper = new HeightWrapper();

    /* get heights of left and right subtrees and their diameters */
    int leftDiameter = getDiameter_helper(root.left, lhWrapper);
    int rightDiameter = getDiameter_helper(root.right, rhWrapper);

    /* calculate root diameter */
    int rootDiameter = lhWrapper.height + rhWrapper.height + 1;

    /* calculate height of current node */
    wrapper.height = Math.max(lhWrapper.height, rhWrapper.height) + 1;

    /* calculate the diameter */
    return Math.max(rootDiameter, Math.max(leftDiameter, rightDiameter));
}

public int getDiameter(BinaryTreeNode root) {
    HeightWrapper wrapper = new HeightWrapper();
    return getDiameter_helper(root, wrapper);
}