title: Count unique words in a long long string
body: <p>Suppose I have an entire one(or two) book in memory and I want to count the number of unique words in it, how do I count it? My naive approach for small string was to:</p>
  
  <pre><code>create a simple hash, place it in array of fixed size, increment array element
  All words for which hash array has 1 in it, are unique.
  </code></pre>
  
  <p>I want a better approach for my really really long string. I am coding in C. One approach I thought would be to using worker threads that work in blocks and combine results. Is there a better algorithm?</p>