**（leetcode_backtracking) Subsets II

Subsets II

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Question Solution 

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,2], a solution is:

[  [2],  [1],  [1,2,2],  [2,2],  [1,2],  []]

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class Solution {    vector<vector<int> > result;    vector<bool> flag;    public:    vector<vector<int> > subsetsWithDup(vector<int> &S) {        if(S.size()==0)            return result;        sort(S.begin(), S.end());                for(int i=0; i<S.size(); i++)            flag.push_back(false);        bk(S, 0);        return result;    }        void bk(vector<int> &S, int index){        if(index==S.size()){            vector<int> singleSulution;            for(int i=0; i<S.size(); i++){                if(flag[i])                    singleSulution.push_back(S[i]);                                }            result.push_back(singleSulution);            return;        }                //flag[index] = false;        bk(S, index+1);                if( index==0 || S[index]!=S[index-1] || (S[index]==S[index-1] && flag[index-1] )){ //判断去重~！            flag[index] = true;            bk(S, index+1);            flag[index] = false;        }    }    };