title: vb.net special permutation of array
body: <p>Let's says I have an array that consists of string like </p>
  
  <pre><code>array = "C-F-A-M"
  </code></pre>
  
  <p>Instead of common permutation's formulas like </p>
  
  <pre><code>**n! / (n-r)**
  </code></pre>
  
  <p>I want the result of array permutation is like this</p>
  
  <pre><code>C-M
  F-M
  A-M
  C-A-M
  C-F-M
  A-F-M
  </code></pre>
  
  <p>My questions is, is there a formulas to create a permutation like that? In vb.net, is there a special method that can create a permutation?</p>
  
  <p>I don't ask for a codes or something, I'm just asking about formulas.</p>