dsa-competitive-programming/leetcode/lc18/4sumPointers.cpp

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        int n = nums.size();
        sort(nums.begin(), nums.end());
        set<vector<int>> set;
        vector<vector<int>> output;
        for(int i=0; i<n-3; i++){
            for(int j=i+1; j<n-2; j++){
                long long newTarget = (long long)target - (long long)nums[i] - (long long)nums[j];
                int low = j+1, high = n-1;
                while(low < high){
                    if(nums[low] + nums[high] < newTarget){
                        low++;
                    }
                    else if(nums[low] + nums[high] > newTarget){
                        high--;
                    }
                    else{
                        set.insert({nums[i], nums[j], nums[low], nums[high]});
                        low++; high--;
                    }
                }
            }
        }
        for(auto it : set){
            output.push_back(it);
        }
        return output;
    }
};

//TC : O(n^3)
//SC : o(n)