letters_numbers_hash

grid = Hash[("A".."Z").to_a.zip(1..27).to_a] # creates a hash where keys are letters, values are numbers. 

def to_numbers
  map {|i| grid.fetch(i)} #converts array of letters to numbers, using grid hash. 
end

def to_letters
  sum.map {|i| grid.key(i)} #convers array of numbers into letters, using grid hash. 
end