Gray Code

题目描述
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

分析：根据格林码的规则递归即可。

代码：

    vector<int> grayCode(int n) {            vector<int> s;    if(n==0) {        s.push_back(0);        return s;    }    if(n==1) {        s.push_back(0);        s.push_back(1);        return s;    }    if(n>=2){        s=grayCode(n-1);        int len=s.size();        int mi=(int)pow(2,n-1);        for(int i=0;i<len;i++){            s.push_back(mi+s[len-i-1]);        }        return s;    }     }