class Solution {

public:

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

if(nums.size() <= 3) return {};

vector<vector<int>> res;

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

int front, back;

for(int i = 0; i < nums.size();) {

for(int j = i + 1; j < nums.size();) {

front = j + 1;

back = nums.size() - 1;

while(front < back) {

int temp = nums[i] + nums[j] + nums[front] + nums[back];

if(temp == target){

vector<int> curr;

curr.push_back(nums[i]);

curr.push_back(nums[j]);

curr.push_back(nums[front]);

curr.push_back(nums[back]);

res.push_back(curr);

front++;

while(front < back && nums[front] == nums[front-1])

front++;

back--;

while(front < back && nums[back] == nums[back+1])

back--;

} else if(temp < target) {

front++;

while(front < back && nums[front] == nums[front-1])

front++;

} else {

back--;

while(front < back && nums[back] == nums[back+1])

back--;

}

}

j++;

while(j < nums.size() && nums[j] == nums[j-1])

j++;

}

i++;

while(i < nums.size() && nums[i] == nums[i-1])

i++;

}

return res;

}

};