leetcode---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 {public:    vector<int> grayCode(int n)     {        vector<int> result;        result.push_back(0);        for(int i=0; i<n; i++)        {            int h = 1 << i;            for(int j = result.size()-1; j >= 0; j--)                result.push_back(h + result[j]);        }        return result;    }};