title: Fast count() intersection of two string arrays
body: <p>I need to count the number of elements corresponding to the intersection of two big arrays of strings and do it very fast.</p>
  
  <p>I am using the following code:</p>
  
  <pre><code>arr1[i].Intersect(arr2[j]).Count()
  </code></pre>
  
  <p>For CPU Time, VS Profiler indicates </p>
  
  <ul>
  <li>85.1% in <code>System.Linq.Enumerable.Count()</code></li>
  <li>0.3%  in <code>System.Linq.Enumerable.Intersect()</code></li>
  </ul>
  
  <p>Unfortunately it might to take hours to do all work.</p>
  
  <p>How to do it faster?</p>