Description

Submission

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> rets;
        rets.push_back(0);
        if(n == 0) return rets;

        for(int i = 0; i < n; ++i) {
            for(int j = rets.size() - 1; j >= 0; --j) {
                rets.push_back(rets[j] | (1<<i));
            }
        }
        return rets;
    }
};