Gray Code

Question

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.

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.

[0,2,3,1] is also a valid gray code sequence according to the above definition.

Thoughts

找到规律，对每一个n，都是在n-1的基础上加上（原来n-1的结果在最高位加1，并reverse)

Solution

class Solution:
    # @param {int} n a number
    # @return {int[]} Gray code
    def grayCode(self, n):
        # Write your code here
        result = [0]
        if n == 0:
            return result

        for i in range(1, n+1):
            tmp = []
            for num in result:
                t = num + 2 ** (i-1)
                tmp.append(t)
            tmp.reverse()
            result += tmp

        return result