title: Most efficient way to determine common elements count across large lists of integers
body: <p>I have a <code>List&lt;List&lt;int&gt;&gt;</code> to which i continuously add new <code>List&lt;int&gt;</code>. But before adding i need to make sure my new list contains <strong>less than <em>n</em></strong> integers that are common to other <code>List&lt;int&gt;</code> in my main list. In other words, no duplicates by taking in consideration a <strong>minimum of <em>n</em></strong> elements.</p>
  
  <p>So if my first list contains { 1, 2, 3, 4, 5 } and my second list { 1, 3, 2, 6, 4 } - this would be a duplicate if <strong><em>n</em> = 4</strong> </p>
  
  <p>I used <code>.Intersect()</code> and got the <code>.Count()</code> while looping through the whole list but that gets really slow when the dataset is larger.</p>
  
  <p>What other efficient options do i have here for checking for these duplicates?</p>
  
  <p>Thanks!</p>