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.

class Solution {

public:
    vector<int> grayCode(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> result;      
        result.push_back(0);  
        for(int i=0; i< n; i++)  
        {  
            int highestBit = 1<<i;  
            int len = result.size();  
            for(int i = len-1; i>=0; i--){  
                result.push_back(highestBit + result[i]);  
            }  
        }  
        return result;  
    }
};