Find the largest palindrome made from the product of two 3-digit numbers

gistfile1.rb

def palindrome?(str); str.reverse == str; end

max = 0
900.upto(999) { |a|
  a.upto(999) { |b|
    max = [max, a * b].max if palindrome?((a * b).to_s)
  }
}
max

array = (900..999).to_a
array.inject([0]) { |i,sum| i += array.map { |n| sum*n } }.select{|v| palindrome?(v.to_s)}.uniq.sort.last