90. Subsets II

class Solution 
{
public:
    vector<vector<int>> subsetsWithDup(vector<int>& nums) 
    {
        vector<vector<int>> res;
        vector<int> cur;
        sort(nums.begin(),nums.end());
        int sz=nums.size();
        backtrack(res,cur,nums,0,sz);
        return res;
    }
    
    void backtrack(vector<vector<int>>& res,vector<int>& cur,vector<int>& nums,int s,int& sz)
    {
        res.push_back(cur);
        for(int i=s;i<sz;i++)
        {
            if(i==s||nums[i]!=nums[i-1])
            {
                cur.push_back(nums[i]);
                backtrack(res,cur,nums,i+1,sz);
                cur.pop_back();
            }
        }
    }
};

加限制条件的回溯法，很典型，具有代表性