3. 25 points] Write a Python function diameter that takes the adjacency list representation of a connected undirected graph and returns the diameter, which is defined as the maximum over all pairs of nodes of the distance (shortest path length) between them. Your program should be a modification of BFS and run in polynomial time. Include comments briefly explaining the algorithm. You may assume the graph is connected (otherwise the diameter would be By the way, the diameter of a graph is a measure of the "small world phenomenon". For example, in the Facebook graph (where nodes are people and edges represent friend relation- more precisely, the dianeter of the giant connected component), and the average distance between pairs of people is less than 5