Question

It is easy to implement the algorithm using a single process, however, how can I use multiple processes to do the job?

Here is what I have done so far.

 find_largest([H], _) -> H;
 find_largest([H, Q | T], R) ->
     if H > Q -> find_largest([H | T], [Q | R]);
       true -> find_largest([Q | T], [H | R])
 end.

Thanks

Answer 1

Given how Erlang represents lists, this is probably not a good idea to try and do in parallel. Partitioning the list implies a lot of copying (since they are linked lists) and so does sending these partitions to other processes. I expect the comparison to be far cheaper than copying everything twice and then combining the results.

The implementation is also not correct, you can find a good one in lists.erl as max/1

%% max(L) -> returns the maximum element of the list L

-spec max([T,...]) -> T.

max([H|T]) -> max(T, H).

max([H|T], Max) when H > Max -> max(T, H);
max([_|T], Max)              -> max(T, Max);
max([],    Max)              -> Max.

If by some chance your data are already in separate processes, simply get the lists:max/1 or each of the lists and send them to a single place, and then get the lists:max/1 of the result list. You could also do the comparison as you receive the results to avoid building this intermediate list.