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.
解法：使用递归或者迭代的思想。每次增加一位，最高位就增加了0，后者1.最高位是0的情况就是n-1的解，最高位是1的情况就是n-1的解的倒序加上一个2的指数。
1 public class Solution { 2 List<Integer> before=new ArrayList<>(Arrays.asList(0,1)); 3 int pluss=1; 4 public List<Integer> grayCode(int n) { 5 List<Integer> list=new ArrayList<>(); 6 list.add(0); 7 if (n==0) { 8 return list; 9 } 10 if (n==1) { 11 list.add(1); 12 return list; 13 } 14 list.add(1); 15 for (int i = 1; i < n; i++) { 16 pluss=pluss*2; 17 for (int j = before.size()-1; j >=0 ; j--) { 18 list.add(before.get(j)+pluss); 19 } 20 before=list; 21 } 22 return list; 23 } 24 }
原文：http://www.cnblogs.com/birdhack/p/4012331.html