title: I have a sorted list of key/value pairs, and want to find the values adjacent to a new key
body: <p>I have a list of key/value pairs (probably will be using a SortedList) and I won't be adding new values.  </p>
  
  <p>Instead I will be using new keys to get bounding values.  For example if I have the following key/value pairs: </p>
  
  <pre><code>(0,100) (6, 200), (9, 150), (15, 100), (20, 300) 
  </code></pre>
  
  <p>and I have the new key of 7, I want it to return 200 and 150, because 7 is between 6 and 9.  </p>
  
  <p>If I give 15 I want it to return 100 and 100 (because 15 is exactly 15).  I want something like a binary search.  </p>
  
  <p>Thanks</p>