prob036.rb

#!/usr/bin/env ruby1.9

# Project Euler, Problem 36
#
# The decimal number, 585 = 1001001001 (binary), is palindromic in both
# bases.
#
# Find the sum of all numbers, less than one million, which are palindromic
# in base 10 and base 2.
#
# (Please note that the palindromic number, in either base, may not include
# leading zeros.)
#
# Lawrence Velazquez
# 11 March 2012

class Fixnum
  def to_binary_s
    bits = 63.downto(0).each_with_object("") {|i, str| str << self[i].to_s}
    bits.sub(/^0+/, "")
  end
  
  def bipalindromic?
    return false if self != self.to_s.reverse.to_i
    self == self.to_binary_s.reverse.to_i(2)
  end
end

puts 1.upto(999999).inject(0) {|sum, n| n.bipalindromic? ? sum + n : sum}