new_contents: ```
  The gray code is a binary numeral system where two successive values differ in only one bit.
  
  Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0.
  
  For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:
  
  00 - 0
  01 - 1
  11 - 3
  10 - 2
  Note:
  For a given n, a gray code sequence is not uniquely defined.
  
  For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.
  
  For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.
  ```
  
  class Solution:
      # @param {integer} n
      # @return {integer[]}
      def grayCode(self, n):
          result = []
          for i in xrange(2**n):
              result.append(i>>1 ^ i)
          return result 
          
  def graycode( n):
      return [ (i >> 1 ^ i )for i in xrange(1<<n)]
  print graycode(3)
  
          
  #Conver from Gray Code to Normal Code:
  def graycode(num):
      result = []
      for number in num:
          mask = number >> 1
          while mask != 0:
              number = number ^ mask
              mask = mask >> 1
          result.append(number)
      return result
  
  print graycode([0, 1, 3, 2, 6, 7, 5, 4])
  
  #Reference: http://en.wikipedia.org/wiki/Gray_code        
  
subject: Create Gray_Code.py