Subsets II

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],
  []
]

没有什么区别，就是往前挪两下指针。。。。

class Solution {
public:
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        vector<vector<int> > res;
        vector<int> solution;
        res.push_back(solution);
        if (S.size()==0)
            return res;
        sort(S.begin(), S.end());
        helper(res,solution,S,0);
        return res;
    }


   void helper(vector< vector<int> >& res, vector<int>& solution, vector<int>& input, int level){
    	for (int i=level; i<input.size();i++){
    		solution.push_back(input[i]);
    		res.push_back(solution);
    		helper(res,solution,input,i+1);
    		solution.pop_back();
    		while(i<input.size()-1 && input[i]==input[i+1])
    		    i++;
    	}


    }
};