leetcode 089 —— 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.

思路：n阶格雷码跟n-1阶格雷码有着莫大的联系，前面加0，或者加1 然后上下颠倒排列

class Solution {public:vector<int> grayCode(int n) {vector<int> res={0};for (int i = 0; i < n; i++){int len = res.size();for (int j =len-1 ; j >=0; j--){res.push_back(res[j] + pow(2, i));}}return res;}};