Now that we have looked at marking the object collection in the cache for eviction, let us look at a few techniques to improve the information passed from the garbage collection to the cache. We maintained that the cache need not implement any strategy such as the least-recently-used, time-to-live and such others. The garbage collection already maintains a distinct set of generations and it is grading down the objects and the information passed to the cache need not be a mark to delete. It can be transparent to the cache with all the statistics it gathers during the collection run. Therefore, the cache may be able to determine the next steps even if the garbage collector suddenly disappeared. This means it includes everything from counts of accesses to the object, initialization time, the last modified time and such others. Although we use the term garbage collector, it is really a metadata collector on the object because a traditional garbage collector relied extensively on the root object hierarchy and the scopes introduced by a predetermined set of instructions. Here, we are utilizing the metadata for the policy which the cache need not implement. Therefore, all information from the layer above may be saved so that the cache can use it just the same in the absence of any direct information of which objects to evict. Finally, the service for the cache may be able to bring the policy into the cache layer itself.
Let us now look at the topology of the cache. Initially we suggested that a set of servers can participate in the cache if the objects are distributed among the servers. In such a case, the cache was distributed among n servers as hash(o) modulo n. This had the nasty side-effect that when one or more servers went down or were added into the pool, all the objects in the cache would lose their hash because the variable n changed. Instead consistent hashing came up with the scheme of accommodating new servers and taking old servers offline by arranging the hashes around a circle with cache points.  When a cache is removed or added, the objects with hashes along the circle are moved clockwise to the next cache point. It also introduced “virtual nodes” which are replicas of cache points in the circle. Since the caches may have non-uniform distribution of objects across caches, the virtual nodes have replicas of objects from a number of cache points.
#codingexercise
Find the minimum number of subset elements of an integer array that sum to a given number
This follows the dynamic programming :
return min(1+ recursion_with_the_candidate_and_sum_minus_candidate, recursion_without_candidate_and_same_sum)
We add the validations for the terminal conditions.