[leetcode]Gray Code @ Python

 题意：

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.

  原题地址：https://oj.leetcode.com/problems/gray-code/

解题思路：格雷码的生成，采用数学的方法。

class Solution:
    # @return a list of integers
    def grayCode(self, n):
        res=[]
        size=2**n
        for i in range(size):
            res.append((i>>1)^i) # http://en.wikipedia.org/wiki/Gray_code
        return res

 知识点：Bitwise Operator

https://wiki.python.org/moin/BitwiseOperators
x << y:  (equal to: x * (2**y)  )
Returns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.
x >> y   (equal to: x / (2**y)  )
Returns x with the bits shifted to the right by y places. This is the same as dividing x by 2**y.