classSolution {

vector<vector<int>> res;

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

if(nums.size() <4)return res;

vector<int>quad;

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

kSum(0,4,target,nums,quad);

return res;

}

voidkSum (int index ,int k ,longlong target, vector<int> nums , vector<int>&q)

{

if(k ==2)

{

twoSum(index , target, q , nums);

return;

}

for(int i = index ; i < nums.size() - k +1; i++)

{

if(i > index && nums[i] == nums[i-1])continue;

q.push_back(nums[i]);

kSum(i+1 , k-1 , target-nums[i] , nums , q);

q.pop_back();

}

}

voidtwoSum (int start,longlong target,vector<int>&ans,vector<int>& nums)

{

int lo = start;

int hi = nums.size()-1;

while(lo < hi)

{

int sum = nums[lo]+nums[hi];

if(sum > target) hi--;

elseif (sum < target) lo++;

{

ans.insert(ans.end() , {nums[lo] , nums[hi]});

res.push_back(ans);

stringlongestCommonPrefix(vector<string>& strs) {

string result = strs[0];

int charIndex =0;

ans.pop_back();

ans.pop_back();

lo++;

while (lo < hi && nums[lo] == nums[lo -1]) lo++;

}

}

}

long maxCharIndex = strs[0].length();

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

if (strs[i].length() < maxCharIndex) {

maxCharIndex = strs[i].length();

}

}

while (charIndex < maxCharIndex) {

char prevChar = strs[0][charIndex];

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

if (prevChar == strs[i][charIndex]) {

continue;

}

return result.substr(0, charIndex);

}

++charIndex;

result += prevChar;

}

return result.substr(0, charIndex);

}

};