4Sum.cpp

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