title: Search in ordered list
body: <p>Assume we have a list 0, 10, 30, 45, 60, 70 sorted in ascending order. Given a number X how to find the number in the list immediately below it?</p>
  
  <p>I am looking for the most efficient (<strong>faster</strong>) algorithm to do this, without of course having to iterate through the whole list.</p>
  
  <pre><code>Ex: [0, 10, 30, 45, 60, 70]
  
  Given the number 34, I want to return 30.
  Given the number 30, I want to return 30.
  Given the number 29, I want to return 10.
  </code></pre>
  
  <p>And so forth.</p>