FourSum.cpp

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> ans;

        int n = nums.size();
        for(int i = 0; i < n; i++)
        {
            if(i > 0 and nums[i] == nums[i - 1]) continue;
            for(int j = i + 1; j < n; j++)
            {
                if(j > (i + 1) and nums[j] == nums[j - 1]) continue;
                
                int start = j + 1;
                int end = n - 1;

                while(start < end)
                {
                    long long sum = nums[i];
                    sum += nums[j];
                    sum += nums[start];
                    sum += nums[end];

                    if(sum == target)
                    {
                        ans.push_back({nums[i] , nums[j] , nums[start] , nums[end]});
                        int low = nums[start];
                        int high = nums[end];
                        start++,end--;
                        while(start < end and nums[start] == low) start++;
                        while(start < end and nums[end] == high) end--;
                    }
                    else if(sum > target) end--;
                    else start++;
                }
            }
        }
        return ans;
    }
};