4sum.cpp

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        int n = nums.size();
        sort(nums.begin(), nums.end());
        vector<vector<int>> res;
        set<vector<int>> s;

        for(int i = 0; i < n; i++) {
            for(int j = i + 1; j < n; j++) {
                long long new_target = (long long)target - (nums[i] + nums[j]);
                int l = j + 1, r = n - 1;
                while(l < r) {
                    int sum = nums[l] + nums[r];
                    if(sum > new_target)
                        r--;
                    else if(sum < new_target)
                        l++;
                    else {
                        s.insert({nums[i], nums[j], nums[l], nums[r]});
                        l++;
                        r--;
                    }
                }
            }
        }

        for(auto i: s) {
            res.push_back(i);
        }
        return res;
    }
};