title: Count number of subsets with sum equal to k
body: <p>Given an array we need to find out the count of number of subsets having sum exactly equal to a given integer k.
  Please suggest an optimal algorithm for this problem. Here the actual subsets are not needed just the count will do.</p>
  
  <p>The array consists of integers which can be negative as well as non negative.</p>
  
  <p>Example:
  Array -> {1,4,-1,10,5} abs sum->9
  Answer should be 2 for{4,5} and {-1,10}</p>