Display how many times an integer occurs at each index, within a nested array.

countem.rb

def countem(list_of_lists)
  occurrences = {}
  list_of_lists.each do |inner_list|
    inner_list.each_with_index do |integer, index_of_integer|
      if occurrences.has_key?("#{integer} @ #{index_of_integer}") == false
        # if not there, add it
        occurrences["#{integer} @ #{index_of_integer}"] = 1
      else
        # if there, increment
        occurrences["#{integer} @ #{index_of_integer}"] += 1
      end
    end
  end
  occurrences.each_pair do |key, value|
    p "#{key} -> #{value}"
  end  
end

# Uncomment for testing
# countem([ [1, 2, 3], [3, 3, 4], [1, 3, 1], [1, 3, 4, 2, 1] ])