title: Code Golf: Duplicate Character Removal in String
body: <p>The challenge: The shortest code, by <strong>character count</strong>, that detects and removes duplicate characters in a String. Removal <em>includes ALL instances</em> of the duplicated character (so if you find 3 n's, all three have to go), and original character order needs to be preserved.</p>
  <blockquote>
  <p>Example Input 1:<br />
  nbHHkRvrXbvkn</p>
  <p>Example Output 1:<br />
  RrX</p>
  </blockquote>
  <hr />
  <blockquote>
  <p>Example Input 2:<br />
  nbHHkRbvnrXbvkn</p>
  <p>Example Output 2:<br />
  RrX</p>
  </blockquote>
  <p>(the second example removes letters that occur three times; some solutions have failed to account for this)</p>
  <p>(This is based on <a href="https://stackoverflow.com/questions/1343934/fastest-way-to-implement-duplicate-character-removal-in-string-c">my other question</a> where I needed the fastest way to do this in C#, but I think it makes good Code Golf across languages.)</p>