leetcode89 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 { //列举n为1、2、3等前几种情况，找规律，模拟
public:
    vector<int> grayCode(int n) {
        vector<int> ans;
        ans.push_back(0);
        for(int i=1;i<=n;i++)
            getgray(ans,i);
        return ans;
    }
    void getgray(vector<int>&ans,int i)
    {
        int size=ans.size();
        for(int a=size-1;a>=0;a--)
        {
            ans.push_back(1<<(i-1)|ans[a]);
        }
    }
};