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 - 001 - 111 - 310 - 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.

要求 n == 0 时，返回 0， 有点奇怪。

class Solution {public:vector<int> grayCode(int n) {vector<int> ivec = { 0 };if (n <= 0)return ivec;ivec.push_back(1);int num = 1;for (int i = 1; i < n; i++) {num *= 2;for (int j = ivec.size() - 1; j >= 0; j--) {ivec.push_back(ivec[j] + num);}}return ivec;}};