Problem Recommendations

It doesn't work for challenge problems because I have been scraping data from the plaintext history by looking for "AC"s. Thanks for pointing this out, I will try to get it fixed sometime within the next few days.

My code is available on Github, but it is a little messy right now. github.com/vikhyat/spojtool3

Basically, I get a list of problems solved by several users, and then invert this data to get a list of users who have solved each problem. Then I compute the similarity of problems. (I am using the Sørensen index currently.) For each problem, I compute the similarity with every other problem I know of and store the top few matches. (This data is in similarities.rb.) Once I have the similarities, it is quite straightforward to recommend problems:

def recommendations(user)
  scores = {}
  my_problems = solved_problems(user)
  my_problems.each do |problem|
    similar = $similarities[problem.to_sym]
    for i,j in similar # i is the problem code, j is the similarity
      next if my_problems.include? i.to_s
      scores[i] ||= 0
      scores[i] += j
    end
  end
  scores.sort_by {|k,v| v }.reverse.map {|x| x[0] }[0..19]
end

I have fixed it, it now works for challenge problems too.