leetcode: 89. 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.
#
# For now, the judge is able to judge based on one instance of gray code sequence. 
# Sorry about that.

class Solution():
    def grayCode(self, n):
        return [i >> 1 ^ i for i in range(1 << n)]


if __name__ == "__main__":
    assert Solution().grayCode(0) == [0]
    assert Solution().grayCode(2) == [0, 1, 3, 2]