title: Playfair cipher random key (C#)
body: <p>Need to solve playfair code with shotgnhillclimbing method, Want to do it simple first by generating random key, and then calculating the score by english-book alphabet pair freq.</p>
  
  <p>But I don't know how to produce nonrepeating random key, it's 25! possibilities. so if i use while forever, the possibility of me finding the right key is super small.</p>
  
  <p>How can i produce a key and then ask the compiler to not to use it again?. Do i use list:add or remove? or is there anything else? or probably a string[25!]?</p>