in reply to finding probes with one mutation ?

If you ask homework questions on Perlmonks, the whole idea is not that we write yor homework for you, but rather give you some pointers so you can do it yourself.

So, go back to your previous question and the answers you received and then look at your present code and meditate on:

  1. the use of "use strict; use warnings;"
  2. the benefits of the three-argument open
  3. the use of single quotes against double quotes.
These may look like small insignificant things now, but they are likely to save your skin later when you write larger programs.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In Section Seekers of Perl Wisdom