Kaprekar number

kaprekar.rb

# https://rubymonk.com/learning/books/1-ruby-primer/problems/150-kaprekar-s-number
def kaprekar?(k)
  k_st = k.to_s
  kk = k**2
  kk_st = kk.to_s
  offset_length = kk.to_s.length.odd? ? k_st.length - 1 : k_st.length
  left = kk_st[0, offset_length]
  right = kk_st[offset_length, k_st.length]
  k == left.to_i + right.to_i
end

numbers = [9, 46, 55, 90, 297, 703]
vals = [true, false, true, false, true, true]

vals == numbers.map { |n| kaprekar?(n) }