leetcode89~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.

n位格雷码，是由n-1位格雷码转换成。一部分是n-1位格雷码，另一部分是1<<(n-1)和n-1位格雷码的逆序之和

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