[leetcode ] gray code

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> results;
        do{
            if (n < 0)
                break;
            else if (n == 0)
            {
                results.push_back(0);
                break;
            }
            else
            {
                results = grayCode(n-1);
                int length = results.size();
                for (int i = length -1 ; i >=0 ; i--)
                {
                    results.push_back(results[i] + (1<<(n-1)));
                }
            }
        }while(false);
        return results;
        
    }
};

规律总结 ： http://xiaotongchen.me/posts/47

注意

results.push_back(results[i] + (1<<(n-1)));

开始结果怎么都是错，后来注意到是运算符优先级的问题！！ 注意 + 优先级高于 <<