code: public long computeTotalCombinations() {
  
  		long numerator = a.size();
  		long denominator = k;
  
  		for( int i = 1; i < k; i++ ) {
  			numerator *= a.size()-i;
  			denominator *= k-i;
  		}
  
  		return numerator/denominator;
  	}
docs: The number of combinations is, n!/(k!*(n-k)!, where n is number of elements, k is the number of bins, and
  ! is factorial.
  
  @return Total number