4Sum.cpp

    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> vv;
        sort(nums.begin(),nums.end());
        int n = nums.size();
        for(int i=0;i<n-3;++i){
            if(i>0 && nums[i]==nums[i-1]) continue;
            for(int j=i+1;j<n-2;++j){
                if(j>i+1 && nums[j]==nums[j-1]) continue;
                int k=j+1,l=n-1;
                while(k<l){
                    long long sum = (long long)nums[i]+ nums[j]+ nums[k]+ nums[l];
                    if(sum == target){
                        vv.push_back({nums[i],nums[j],nums[k],nums[l]});
                        while(k<l && nums[k]==nums[k+1]) ++k;
                        while(l>k && nums[l]==nums[l-1]) --l;
                        ++k;
                        --l;
                    }
                    else if(sum<target) ++k;
                    else --l;
                }
            }
        }
        return vv;
    }