class Solution {

vector<vector<int>> fourSum(vector<int>& nums, int target) {

vector<vector<int>> result;

int n = nums.size();

if(n < 4) return result;

sort(nums.begin(), nums.end());

for(int i = 0; i < n - 3; i++) {

if(i > 0 && nums[i] == nums[i - 1]) continue; // skip duplicates for i

for(int j = i + 1; j < n - 2; j++) {

if(j > i + 1 && nums[j] == nums[j - 1]) continue; // skip duplicates for j

int left = j + 1;

int right = n - 1;

while(left < right) {

long long sum = (long long)nums[i] + nums[j] + nums[left] + nums[right];

if(sum == target) {

result.push_back({nums[i], nums[j], nums[left], nums[right]});

// skip duplicates for left

while(left < right && nums[left] == nums[left + 1]) left++;

// skip duplicates for right

while(left < right && nums[right] == nums[right - 1]) right--;

left++;

right--;

}

else if(sum < target) left++;

else right--;

}

}

}

return result;

}

};