title: Lambda expression for getting indexes of list items conditionally
body: <p>I have a <code>List&lt;bool&gt;</code>. I need to get the indexes of top n items where item value = true.</p>
  
  <p>For example the following list items(bool)</p>
  
  <pre><code>10011001000
  
  TopTrueIndexes(3) = The first 3 indexes where bits are true are 0, 3, 4 
  TopTrueIndexes(4) = The first 4 indexes where bits are true are 0, 3, 4, 7 
  </code></pre>
  
  <p>How can I write a lambda for this?</p>