Gray Code


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.
Solution:
There is a good instruction on Wiki about how to generate a gray code recursively.



The following code passes LeetCode Online Large Judge.
Update: Thank Yao for providing a much neater version Update: my own solution when I redo this problem (2013.05.17). NO RECURSION AND BUG FREE!

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