title: Set difference in C++
body: <p>If I know that one set is a subset of another set and I would like to find the difference, what's the most efficient way to do this?</p>
  
  <p>ex.
  PSEUDO CODE</p>
  
  <pre><code>&gt; set&lt;int&gt; set1 = {1 2 3 4 5 6 7 8 9 10}
  &gt; set&lt;int&gt; set2 = {5 6 7}
  </code></pre>
  
  <p>I want to subtract <code>set2</code> from <code>set1</code>:</p>
  
  <p>The answer here would be </p>
  
  <pre><code>{1 2 3 4 8 9 10}
  </code></pre>