4Sum

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
       vector<vector<int>> res;
       int i,j,k,l;
       if(nums.size()<4) return res;
       sort(nums.begin(),nums.end());
       for( i=0;i<nums.size()-3;i++)
       {
           if(i>0 &&nums[i]==nums[i-1]) continue;
           for(j=i+1;j<nums.size()-2;j++)
           {
               if(j>i+1 &&nums[j]==nums[j-1]) continue;
                k=j+1;
                l=nums.size()-1;
               while(k<l)
               {
                 while(k<l &&nums[i]+nums[j]+nums[k]+nums[l]<target) k++;
                 while(k<l &&nums[i]+nums[j]+nums[k]+nums[l]>target) l--;
                 if(k<l &&nums[i]+nums[j]+nums[k]+nums[l]==target)
                 {
                     vector<int>tmp;
                     tmp.push_back(nums[i]);
                     tmp.push_back(nums[j]);
                     tmp.push_back(nums[k]);
                     tmp.push_back(nums[l]);
                     res.push_back(tmp);
                     k++;
                     while(nums[k]==nums[k-1]&&k<l) k++;
                     l--;
                     while(nums[l]==nums[l+1]&&k<l) l--;
                 }
               }
           }
          
       }
       return res;
    }
};