palindrome

palindrome.rb

def palindrome(first_number, second_number=first_number) 
  if first_number > second_number
    raise ArgumentError.new 'First number cannot be greater than second number'
  end    


  palindromes = []

  (first_number..second_number).each do |number|
    (first_number..second_number).each do |number2|
      product = number * number2
      if product.to_s.split("") == product.to_s.split("").reverse && !(palindromes.include?(product))
        palindromes << product
      end
    end
  end
  palindromes.sort
end

palindrome_spec.rb

require 'rspec'
require 'palindrome'

describe 'palindrome' do
  it 'raises an exception for non-number data' do
    expect {palindrome(1, 'foo')}.to raise_exception
    expect {palindrome(1, [])}.to raise_exception
    expect {palindrome(true, 'foo')}.to raise_exception
  end

  it 'raises an exception if the first argument is greater than the second' do
    expect {palindrome(3, 2)}.to raise_exception
  end

  it 'finds palindromes for a basic range' do
    palindrome(10, 12).should eq [121]
  end

  it 'doesn\'t repeat matches' do
    palindrome(2, 11).should eq [4, 6, 8, 9, 22, 33, 44, 55, 66, 77, 88, 99, 121]
  end

  it 'returns an ordered array' do
    palindrome(2, 4).should eq [4, 6, 8, 9]
  end
end