My solution for Sophie's Extreme Memory challenge (https://github.com/sophietk/xke-memory-server)

extreme_memory_client.rb

# This is the raw code as it was at the end of the session.
#
# In retrospect, the following could be improved:
# * @to_see is useless, two simple nested loops would work (or maybe keep it but shuffle it)
# * handle throttling better (instead of a lame DELAY)
# * I forgot to handle the case when I pick a pair by chance!
# * monitor game progress to avoid losing too many points
require "rest_client"
require "json"

ROOT = "http://10.1.1.46:3000"
BOARD_SIZE = 8
DELAY = 1.0

class Game
  def initialize
    @to_see = []
    (0..BOARD_SIZE-1).each do |x|
      (0..BOARD_SIZE-1).each do |y|
        @to_see.push [x, y]
      end
    end

    # sorted by symbol & color
    @seen = {}

    # knowns pairs to try on next turns
    @next_pairs = []
  end

  def play
    puts "Start playing"

    while (true) do
      if @next_pairs.size > 0
        pick(@next_pairs.pop)
      else
        card1 = @to_see.pop
        card2 = @to_see.pop
        status = pick([card1, card2])
        details1 = status["turn"]["cards"][0]
        details2 = status["turn"]["cards"][1]
        process(card1, details1)
        process(card2, details2)
      end
      sleep(DELAY) if DELAY
    end
  end

  def pick(cards)
    puts "pick #{cards}"
    response = RestClient.post "#{ROOT}/play",
               "[[#{cards[0][0]}, #{cards[0][1]}], [#{cards[1][0]}, #{cards[1][1]}]]",
               :content_type => :json
    puts "response: #{response}"
    JSON.parse(response)
  end

  def process(coords, details)
    puts "Process result for #{coords} #{details}"
    @to_see.delete(coords)
    if not details["found"]
      key = [details["symbol"], details["color"]]
      if @seen[key]
        puts "Already seen #{key} at #{@seen[key]} => PROFIT!"
        @next_pairs.push( [coords, @seen[key]] )
        @seen.delete key
      else
        puts "Never seen #{key} before, remember position"
        @seen[key] = coords
      end
    end
  end
end

register_status = RestClient.post "#{ROOT}/scores/register", "omichallat@xebia.fr", :content_type => :json
puts "Registered: #{register_status}"

Game.new().play()