I've just done (part of) Advent of Code 2018 q9 in #Haskell.  My first attempt, I thought was elegant and readable, but consumed all RAM in the universe.  My second attempt, was more nuanced, throwing away all the things the solution did not really need, and this at least completed, however it takes 11 min to run.  

The second part of the question expands the problem size by a factor of 100.  

Need to think about this again!