12. A data stream is an extremely long sequence of items that you can only read only once, in order. A good example of a data stream is the sequence of packets that pass through a router. Data stream algorithms must process each item in the stream quickly, using very little memory; there is simply too much data to store, and it arrives too quickly for any complex computations. Every data stream algorithm looks roughly like this: DOSOMETHINGINTERESTING(stream S): repeat x next item in S (do something fast with x)) until S ends return ((something) and analyze an algorithm that chooses one element uniformly at random from a data stream, without knowing the length of the stream in advance. Your algorithm should Describe spend O(1) time per stream element and use O(1) space (not counting the stream itse