title: Explain the use of a bit vector for determining if all characters are unique
body: <p>I am confused about how a bit vector would work to do this (not too familiar with bit vectors). Here is the code given. Could someone please walk me through this?</p>
  
  <pre><code>public static boolean isUniqueChars(String str) {
      int checker = 0;
      for (int i = 0; i &lt; str.length(); ++i) {
          int val = str.charAt(i) - 'a';
          if ((checker &amp; (1 &lt;&lt; val)) &gt; 0) return false;
          checker |= (1 &lt;&lt; val);
      }
      return true;
  }
  </code></pre>
  
  <p>Particularly, what is the <code>checker</code> doing?</p>