class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        set<vector<int>> res;   //use set for drop the repete
        if(nums.size()<4) return {};
        sort(nums.begin(),nums.end());
        for(int i=0;i<nums.size()-3;i++){
            for(int j=i+1;j<nums.size()-2;j++){
                if(j>i+1 && nums[j]==nums[j-1]) continue;
                int m=j+1,n=int(nums.size())-1;
                
                while(m<n){
                    int sum=nums[i]+nums[j]+nums[m]+nums[n];
                    if(sum==target){
                            vector<int> tmp{nums[i],nums[j],nums[m],nums[n]};
                        res.insert(tmp);
                        m++;n--;
                    }
                    else if(sum<target) m++;
                    else n--;
                }
            }
        }
        return vector<vector<int>>(res.begin(),res.end());
    }
};