<p>Given an array <code>nums</code> of <code>n</code> integers, return <em>an array of all the <strong>unique</strong> quadruplets</em> <code>[nums[a], nums[b], nums[c], nums[d]]</code> such that:</p>

<ul>
	<li><code>0 &lt;= a, b, c, d&nbsp;&lt; n</code></li>
	<li><code>a</code>, <code>b</code>, <code>c</code>, and <code>d</code> are <strong>distinct</strong>.</li>
	<li><code>nums[a] + nums[b] + nums[c] + nums[d] == target</code></li>
</ul>

<p>You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,0,-1,0,-2,2], target = 0
<strong>Output:</strong> [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [2,2,2,2,2], target = 8
<strong>Output:</strong> [[2,2,2,2]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 200</code></li>
	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>-10<sup>9</sup> &lt;= target &lt;= 10<sup>9</sup></code></li>
</ul>

class Solution {
public:

    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> answer;
        std::set<vector<int>> map;
        sort(nums.begin(), nums.end());
        if(nums.size() < 4){
            return answer;
        }
        /*
        *  n^4;
        */
        // for(int i =0; i < nums.size()-3; i++){
        //     for(int j =i+1; j < nums.size()-2; j++){
        //         for(int z = j +1; z < nums.size()-1; z++){
        //             for(int k = z+1; k < nums.size(); k++){
        //                 int sum = nums.at(i) + nums.at(j) + nums.at(z) + nums.at(k);
        //                 vector<int> elem = {nums.at(i), nums.at(j), nums.at(z), nums.at(k)};
        //                 if(sum == target and map.find(elem) == map.end()){
        //                     map.insert(elem);
        //                     answer.push_back(elem);
        //                 }
        //             }
        //         }
        //     }
        // }
        std::map<long long,int> elements;
        for(int i=0; i < nums.size(); i++){
            elements[nums.at(i)] = i;
        }
        for(int i =0; i < nums.size()-3; i++){
            for(int j =i+1; j < nums.size()-2; j++){
                for(int z = j +1; z < nums.size()-1; z++){
                    long long find = (long long)target - ((long long)nums.at(i) + (long long)nums.at(j) + (long long)nums.at(z));
                    
                    if(elements.find(find) != elements.end()){
                        vector<int>elem = {nums.at(i), nums.at(j), nums.at(z), (int)find};
                        if(elements[find] > z){
                            if(map.find(elem) == map.end()){
                                map.insert(elem);
                                answer.push_back(elem);
                            }
                        }
                    }
                }
            }
        }
        return answer;
    }
};
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