/*
 *  Cache class keeps a hashmap where it 
 *  stores the number of the bucket that holds
 *  the major coreset and the coreset itself
 *  r is the merge threshold in this case
 *  we use r = 2 since we implemented an 2-way 
 *  coreset tree 
 */

/**
  * Implements the CachedKM++ algorithm for data streams. CachedKM++ computes a
  * small (weighted) sample of the stream by using <i>coresets</i> from cache
  * to reduce the number of coresets needed for a merge step, and then uses
  * it as an input to a k-means++ algorithm. It uses a data structure called
  * <tt>BucketManager</tt> to handle the coresets.
  *
  * <p>It uses the following options:
  * <ul>
  *  <li> Number of microclusters (<b>-m</b>)
  *  <li> Initial buffer size (<b>-b</b>)
  *  <li> Size of coresets (<b>-s</b>)
  *  <li> Learning window (<b>-w</b>) * </ul>
  */

prevent sum from NaN when funcost is zero.  splitCoresetTree needed more cases when leaf has no elements

Stream dm 100