title: Telephone Number to Words - Permutation - C#
body: <p>I was asked on an interview: Given a phone number, say 652-7872, print out all possible permutations of the words that it can spell.</p>
  
  <pre><code>2-ABC, 
  3-DEF, 
  4-GHI, 
  5-JKL,
  6-MNO,
  7-PQRS,
  8-TUV,
  9-WXYZ,
  0-O
  </code></pre>
  
  <p>For example, one permutation of 652-7872 is JGAJAPP.</p>
  
  <p>I have seen similar questions answered, however, the solutions either aren't the letter individually OR the letters are random through out the whole string.  </p>
  
  <p>This question, I believe, is asking for </p>
  
  <pre><code>For position 0 of the phone number string (652-7872), 6 - the only possible letter options are "MNO"
  For position 1 of the phone number string (652-7872), 5 - the only possible letter options are "JKL"
  For position 2 of the phone number string (652-7872), 2 - the only possible letter options are "ABC"
  </code></pre>
  
  <p>A short version of possible outcomes for the first 3 #'s would be:</p>
  
  <pre><code>MJA
  MJB
  MJC
  MKA
  MKB
  MKC
  MLA
  MLB
  MLC
  </code></pre>
  
  <p>Would someone tell me how to solve this in C#?  And I'd be interested in how long it takes you.</p>