title: How can i interleave elements of 2 lists in scala
body: <p>I'd like to combine two Lists of arbitrary length in such a way that elements from the 2nd List are inserted after every n-th element into the 1st List. If the 1st List length is less than n, no insertion results.</p>
  
  <p>So having </p>
  
  <pre><code>val a = List(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)
  val b = List(101,102,103)
  val n = 3 
  </code></pre>
  
  <p>I want the resulting List to look like this:</p>
  
  <pre><code>List(1,2,3,101,4,5,6,102,7,8,9,103,10,11,12,13,14,15)
  </code></pre>
  
  <p>I have this working using a <code>foldLeft</code> on <code>a</code>, but I'm wondering how the same logic could be accomplished using Scalaz?</p>
  
  <p>Thanks for everyone's answers. They were all helpful to me !</p>