title: is there a map that will supply me hashing in both direction?
body: <p>I hold the following map</p>
  
  <pre><code>      Map&lt;Integer, List&lt;String&gt;&gt;
  </code></pre>
  
  <p>when I add a new string to a certain int I just add it to the list of that int value in my map.<br>
  Now, I also need to remove it from the last list it was located in.<br>
  I will elaborate for a second :<br>
  It is not the same instance of the string. I get an int and a  String, I need to add it and remove it from the former List in the map that held the same string value.</p>
  
  <p>This means that I need to hold another map of String to Integer ?<br>
  Do I need to maintain two collections?<br>
  thanks.</p>