title: How to find all possible strings after deleting k number of characters from the given string?
body: <p>For example we have a string s = "stackoverflow" .if we delete <strong>one</strong> character then we get "tackoverflow", "sackoverflow", "stckoverflow" ... and so on.
  How to get all possible strings when we delete k number of characters where k &lt; len(s). </p>
  
  <p>We can do by for loop for given exact number of characters to delete and string.But how to do it when number of characters to delete is not fixed.</p>