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：

 /**
      * 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.
      * Solution : find the rule!!!!
      * @param n
      * @return
      */
     public ArrayList<Integer> grayCode(int n) {
         ArrayList<Integer> r = new ArrayList<Integer>();
         r.add(0);
         if(n == 0)
             return r;
         r.add(1);
         if(n == 1)
             return r;
         for(int m = 1;m<n;m++){
             int cur_size = r.size();
             int base = (int) Math.pow(2, m);
             for(int i = cur_size - 1;i>=0;i--){
                 r.add(r.get(i)+base);
             }
         }
         return r;
     }