"""
    longest path between two points :::
                    - for any node 'u', if node 'x' is the farthest node then 'x' is one of the endpoints
                        in the longest path.

                    So solution,
                        For any node 'u', find its farthest node 'x' and then
                        find the farthest node to 'x', node 't',

                        d(x, t) is answer

"""






