static int max_difference = 0;
int solve (node *root)
{
    int left_depth = 0, right_depth = 0, difference;

    if (!root)
        return 0;

    if (root -> get_left()) {
        left_depth = get_depth(root -> get_left());
        solve(root -> get_left());
    }
    if (root -> get_right()) {
        right_depth = get_depth(root -> get_right());
        solve(root -> get_right());
    }

    if ((difference = abs(left_depth - right_depth)) > max_difference)
        max_difference = difference;

    return max_difference;
}


static int len = -1, max_len = 0;
int get_depth (node *root)
{
    if (!root)
        return 0;

    ++len;
    if (!(root -> get_left()) && !(root -> get_right())) {
        if (len > max_len)
            max_len = len;
    }
    else if (root -> get_left())
        solve(root -> get_left());
    if (root -> get_right())
        solve(root -> get_right());

    --len;

    return max_len;
}