LeetCode 89. 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.

格雷编码，一次只能改变一位，给出所有的数字

其实是把一位遍历完后，在倒着把每个数字加上新的位

public class Solution {
    public List<Integer> grayCode(int n) {
        List<Integer>res = new ArrayList<Integer>();
        if(n<0)return res;
        if(n==0){
            res.add(0);
            return res;
        }
        res.add(0);
        res.add(1);
        for(int i=2;i<=n;i++){
            int size = res.size();
            for(int j=size-1;j>=0;j--){
                res.add(res.get(j)+(1<<(i-1)));
            }
        }
        return res;
    }
}