title: inserting char into a string in asc order by binary seach
body: <p>I have some problem with insertion a char into an string in ascending order.</p>
  
  <p>for example</p>
  
  <pre><code>str = ""
  insert c
  str = "c"
  insert a
  str = "ac"
  insert d
  str="acd"
  
  etc.
  </code></pre>
  
  <p>I need to implement it with binary search, so find the place where to put by binary search, then put it.</p>
  
  <p>If you know some good snippet to use, I would appreciate.</p>