Leetcode: 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, 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.

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Solution 1

Get idea from here1, here2

class Solution(object):    def grayCode(self, n):        """        :type n: int        :rtype: List[int]        """        if n==0:            return [0]        res = []        temp = self.grayCode(n-1)        high = 1<<(n-1)        result = temp[:]        for ind in range(len(result)-1,-1,-1):            result.append( high+temp[ind] )        return result

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Solution 2

class Solution(object):    def grayCode(self, n):        """        :type n: int        :rtype: List[int]        """        if n==0:            return [0]        res = []        num = 1<<n        for ind in range(num):            res.append((ind>>1)^ind)        return res