78. Subsets

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经典的回溯法

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int>> result;
        if(nums.empty()) return result;
        vector<int> list;
        dfs(0, result,list,nums);
        return result;
        
    }
private:
    void dfs(int pos, vector<vector<int>>& result,  vector<int>& list, vector<int>& nums){
        result.push_back(list);
        for(int i = pos; i < nums.size(); i++){
            list.push_back(nums[i]);
            dfs(i+1, result, list, nums);
            list.pop_back();
        }
    }
};