1+ class Solution {
2+ public:
3+ vector<vector<int >> fourSum (vector<int >& nums, int target) {
4+ vector<vector<int >> result;
5+ int n = nums.size ();
6+ if (n < 4 ) return result;
7+ 8+ sort (nums.begin (), nums.end ());
9+ 10+ for (int i = 0 ; i < n - 3 ; i++) {
11+ if (i > 0 && nums[i] == nums[i - 1 ]) continue ; // skip duplicates for i
12+ 13+ for (int j = i + 1 ; j < n - 2 ; j++) {
14+ if (j > i + 1 && nums[j] == nums[j - 1 ]) continue ; // skip duplicates for j
15+ 16+ int left = j + 1 ;
17+ int right = n - 1 ;
18+ 19+ while (left < right) {
20+ long long sum = (long long )nums[i] + nums[j] + nums[left] + nums[right];
21+ 22+ if (sum == target) {
23+ result.push_back ({nums[i], nums[j], nums[left], nums[right]});
24+ 25+ // skip duplicates for left
26+ while (left < right && nums[left] == nums[left + 1 ]) left++;
27+ // skip duplicates for right
28+ while (left < right && nums[right] == nums[right - 1 ]) right--;
29+ 30+ left++;
31+ right--;
32+ }
33+ else if (sum < target) left++;
34+ else right--;
35+ }
36+ }
37+ }
38+ return result;
39+ }
40+ };
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