gistfile1.rb

# STEP 1
string = "iirytroyppytpeppowuiyoiuypipiyuyotyoiwiytorouqyiepyirueuiprpptwyiroqwtuyipourrrourorwipowiorutpwtwruuioquteorioriyutwqyyprptuqqquuituyywyuoewtrppqwrtiiruirpwyptpuoyyoeyerpqiotuieripurouwuwyuwrworowitoepoypeipeypiireeorrwripuuteoitpuutturruwiyryeetyrioweytueqrrrtotrpiqetoyepoipiwrwpppiritupwipruooiepoweypiuwrqywuuwyiroqpqpruioopuiuerputpwwuuiqwpiroewrtwiqerteoyeqtutwoeoipioiuqiiiouuoqtuuwtuwiiqwppqitywuqpuutrqiyoeuuutwrwtoqrqyoeyoiporuuioiwryoeruypreprqroiyuqwtuyoytoerwqryeeripryieypiwqirtriurueypiuyuypriuiwptywppupoioyrewooytreteeriiwroietuwypieeeeeqpiiiwrirtppoeyiwpooyyporpruwuoriiyowuytiwpwpryeywotoyirqypyypoeptiuwwoyprquoetepptorwiewprpiywwtuieeiweytrrwiqtwotioryoiptyyyuriiqiyroeeiqepwteuwptpruuypipieuoiiuuweeuryuuowporrooyywyyrryriqyirooitirueruptotpryoqtipippyptiurwyiryooywtryyuurtrutwqiqiiiqwouyeooueoturuowiuwrtruwwiupwopwweoo"

letters = %w(q w e r t y u i o p)
map = {}
letters.each_with_index { |letter, index| map[letter] = index }

numbers = string.split('').map {|letter| map[letter] }

# STEP 2
number_pairs = []
pair_buffer = []
numbers.each do |number|
  if pair_buffer.length == 2
    number_pairs << pair_buffer
    pair_buffer = []
  end
  pair_buffer << number
end

counts = {}
number_pairs.each {|pair| counts[pair] = counts[pair] ? counts[pair]+1 : 1 }

unique_pairs = counts.select {|k,v| v == 1 }.map {|k| k[0] }

# STEP 3-ish
string = ''
number_pairs.each do |pair|
  if unique_pairs.include?(pair)
    string << (pair[0] + pair[1]).to_s
    unique_pairs = unique_pairs - pair
  end
end

puts string