title: All of the option to replace an unknown number of characters
body: <p>I am trying to find an algorithm that for an unknown number of characters in a string, produces all of the options for replacing some characters with stars.</p>
  
  <p>For example, for the string "abc", the output should be:</p>
  
  <pre><code>*bc   
  a*c  
  ab*  
  **c  
  *b*  
  a**
  ***  
  </code></pre>
  
  <p>It is simple enough with a known number of stars, just run through all of the options with for loops, but I'm having difficulties with an all of the options.</p>