class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        vector<vector<int>> ret;
        int len = nums.size(), memi;
        for (int i = 0; i < len - 3; ) {
            memi = nums[i];
            if (1LL * nums[i] + nums[i+1] + nums[i+2] + nums[i+3] > target) {
                while (i < len - 3 && nums[i] == memi) i++;
                continue;
            }
            int mem;
            for (int j = i + 1; j < len - 2; ) {
                mem = nums[j];
                int k = j + 1, l = len - 1;
                while (k < l) {
                    long long sum = 1LL * nums[i] + nums[j] + nums[k] + nums[l];
                    if (sum < target) {
                        int temp = nums[k];
                        while (k < l && nums[k] == temp) k++;
                    }
                    else if (sum > target) {
                        int temp = nums[l];
                        while (k < l && nums[l] == temp) l--;
                    }
                    else {
                        ret.push_back({nums[i], nums[j], nums[k], nums[l]});
                        int temp = nums[k];
                        while (k < l && nums[k] == temp) k++;
                        temp = nums[l];
                        while (k < l && nums[l] == temp) l--;
                    }
                }
                while (j < len - 2 && nums[j] == mem) j++;
            }
            while (i < len - 3 && nums[i] == memi) i++;
        }
        return ret;
    }
};