title: Finding a set of nodes which are one-hop neighbors of each other in an adjacency matrix
body: <p>For a given undirected graph with <code>N</code> nodes and its adjacency matrix, suppose that there is at least one set of <code>n</code> nodes in which every member node is a one-hop neighbor of the others in the set. (<code>n</code> &lt;&lt; <code>N</code>)</p>
  
  <p>In this situation, what is an algorithm to find such a set of nodes?</p>
  
  <p>For example, this is <a href="https://gist.github.com/gsongsong/94b7b3aff38d63db163d" rel="nofollow">a sample adjacency matrix (link: GitHub Gist)</a> with <code>42</code> nodes. And it is known that there is a set in which <code>3</code> nodes are one-hop neighbors of each other. Then, what is the composition of the set?</p>
  
  <p>My final goal is to do this procedure with about <code>450</code> nodes to find a set containing <code>9</code> one-hop neighbor nodes. Thus, I am looking for a solution that is scalable and efficient.</p>