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.

http://oj.leetcode.com/problems/gray-code/

Solution:

See the wiki page of gray code, http://en.wikipedia.org/wiki/Gray_code

We can find that nth gray code is n XOR (n/2). 

https://github.com/starcroce/leetcode/blob/master/gray_code.cpp

// 32 ms for 12 test cases
// binary to gray: G(n) = (B(n)/2) XOR B(n)
class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> res;
        int size = 1 << n;
        for(int i = 0; i < size; i++) {
            res.push_back((i/2)^i);
        }
        return res;
    }
};