title: Design an algorithm, find the most frequently used word in a book
body: <p>An interview question:</p>
  
  <p>Find the most frequently used word in a book.</p>
  
  <p>My idea: </p>
  
  <p>Use a hash table, traverse and mark the hash table. </p>
  
  <p>If the book's size is known, if  any word is found to be used > 50%, then skip any new words in the following traversal and only count old words.  What if the book size is unknown?</p>
  
  <p>It is O(n) and O(n) time and space. </p>
  
  <p>Any better ideas? </p>
  
  <p>Thanks</p>