In general, one useful approach is to pass a length to the 'counted string' function one smaller than the size of the buffer and then explicitly assign zero to the last character in the buffer.

The client writes the string to be counted into memcached, and the worker uses the ID supplied by the client to read the string, count the words, then writes the information back to memcached.

Thus, two different sequence of "buy" days could produce the same string of decreasing prices and be counted as only a single solution.