title: Finding negative cycle in undirected graph
body: <p><em>I tried googling it up, but nothing of value pops up.</em> </p>
  
  <p>The graph:</p>
  
  <ul>
  <li>is undirected.</li>
  <li>is represented as directed graph with double edges.</li>
  <li><strong>may</strong> contain edges with negative weights.</li>
  </ul>
  
  <p>I know I can use Bellman-Ford to solve this in the directed case, but with undirected edges it will just return single edges (2-cycles) as its output. I need to find a cycle of size > 2.</p>
  
  <p>Also, the algorithm is supposed to have run-time complexity O(V*E) and memory complexity O(V).</p>