LeetCode OJ - Gray Code

这道题就是找规律啊！！！

想想啊，11和10是可以连续的，那么10和11也是可以连续的。

下面是AC代码：

 1  /**

 2       * The gray code is a binary numeral system where two successive values differ in only one bit.

 3       * 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.

 4       * For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

 5       * 00 - 0

 6       * 01 - 1

 7       * 11 - 3

 8       * 10 - 2

 9       * Note:

10       * For a given n, a gray code sequence is not uniquely defined.

11       * For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

12       * For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

13       * Solution : find the rule!!!!

14       * @param n

15       * @return

16       */

17      public ArrayList<Integer> grayCode(int n) {

18          ArrayList<Integer> r = new ArrayList<Integer>();

19          r.add(0);

20          if(n == 0)

21              return r;

22          r.add(1);

23          if(n == 1)

24              return r;

25          for(int m = 1;m<n;m++){

26              int cur_size = r.size();

27              int base = (int) Math.pow(2, m);

28              for(int i = cur_size - 1;i>=0;i--){

29                  r.add(r.get(i)+base);

30              }

31          }

32          return r;

33      }