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, find the sequence of gray code. A gray code sequence must begin with
0 and with cover all 2n integers.
For a given
n, a gray code sequence is not uniquely defined.
[0,2,3,1] is also a valid gray code sequence according to the above definition.
n = 2, return
[0,1,3,2]. Its gray code sequence is:
00 - 0 01 - 1 11 - 3 10 - 2