title: Find number of characters mutual between two strings in C#
body: <p>I am looking for a method that will take two strings and return the number of characters that are common to both e.g.:</p>
  
  <p>"G010" &amp; "G1820A" should return 3 as the G, 0 and 1 chars exist in both.</p>
  
  <p>If a char exists twice in both they should be counted separately as follows:</p>
  
  <p>"G12AA" &amp; "GAA2" should return 4 as the G, A, A and 2 characters exist in both.</p>
  
  <p>Any help with this? Google searches haven't been too helpful thus far.</p>