[Leetcode] 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.

 

Solution:

参考了大神的代码

http://fisherlei.blogspot.com/2012/12/leetcode-gray-code.html

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

确实，如果像第一次做的时候用数学方法来做的话，interview也肯定答不出来啊