Given an adjacency-list representation of a multigraph G =(V,E), describe an O(V + E)-time algorithm to compute the adjacency-list representation of the equivalent undirected graph G' = (V, E'), where E' consists of the edges in E with all multiple edges between two vertices replaced by a single edge and with all self-loops removed. Find underlying simple graph of a multigraph. Solve this problem without using hashing.