Given an adjacency list representation undirected graph. Write a function to count the number of edges in the undirected graph.
Expected time complexity : O(V)
Idea is based on Handshaking Lemma. Handshaking lemma is about undirected graph. In every finite undirected graph number of vertices with odd degree is always even. The handshaking lemma is a consequence of the degree sum formula (also sometimes called the handshaking lemma)
So we traverse all vertices, compute sum of sizes of their adjacency lists, and finally returns sum/2. Below c++ implementation of above idea
Time Complexity : O(V)
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