78.cpp

// dfs_recursion.cpp
class Solution {
    void dfs(vector<int>& cur, vector<vector<int>>& res, vector<int>& nums,
             int i) {
        if (nums.size() == i) {
            res.push_back(cur);
            return;
        }
        cur.push_back(nums[i]);
        dfs(cur, res, nums, i + 1);
        cur.pop_back();
        dfs(cur, res, nums, i + 1);
    }

public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<int> cur;
        vector<vector<int>> res;
        dfs(cur, res, nums, 0);
        return res;
    }
};
// smart_iteration.cpp
class Solution2 {
public:
    vector<vector<int>> subsets(vector<int>& S) {
        sort(S.begin(), S.end());
        int elem_num = S.size();
        int subset_num = pow(2, elem_num);
        vector<vector<int>> subset_set(subset_num, vector<int>());
        for (int i = 0; i < elem_num; i++)
            for (int j = 0; j < subset_num; j++)
                if ((j >> i) & 1)
                    subset_set[j].push_back(S[i]);
        return subset_set;
    }
};