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class Solution {
public:vector<vector<int>> subsets(vector<int>& a) {int n = a.size();vector<vector<int>> ans;vector<int> tmp;auto dfs = [&](this auto&& self, int it) -> void{if (it == n) {ans.emplace_back(tmp);return;}self(it + 1);tmp.emplace_back(a[it]);self(it + 1);tmp.pop_back();};dfs(0);return ans;}
};