class Solution {public:    vector<vector<int> > subsetsWithDup(vector<int> &S) {        int len = S.size();        vector<vector<int> > res;        vector<int> subset;        if (len < 1) {            res.push_back(subset);            return res;        }        sort(S.begin(), S.end());        vector<int> stat;        vector<int> nums;        int count = 1;        int cur = S[0];        int last = cur;        for (int i=1; i<len; i++) {            cur = S[i];            if (cur != last) {                stat.push_back(count);                nums.push_back(last);                last = cur;                count = 0;            }            count++;        }        stat.push_back(count);        nums.push_back(last);        dfs(nums, stat, res, subset, 0);    }    void dfs(vector<int> &nums, vector<int> &stat, vector<vector<int> > &res, vector<int> &subset, int k) {        if (k >= nums.size()) {            res.push_back(subset);            return;        }        int cnt = stat[k];        int old = subset.size();        for (int i=0; i <= cnt; i++) {            dfs(nums, stat, res, subset, k + 1);            subset.push_back(nums[k]);        }        subset.resize(old);    }};