<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>> threeSum(vector<int>& nums, long long target, int first){
        vector<vector<int>> ans;
        for(int i = first; i<nums.size();i++){
            int f = i+1, l = nums.size()-1;
            vector<int> a;
            a.push_back(nums[i]);
            while(f<l){
                if((long long)nums[f]+(long long)nums[l]>target-(long long)nums[i]) l--;
                else if((long long)nums[f]+(long long)nums[l]<target-(long long)nums[i]) f++;
                else{
                    a.push_back(nums[f]);
                    a.push_back(nums[l]);
                    ans.push_back(a);
                    a.pop_back();
                    a.pop_back();
                    f++;
                    l--;
                }
            }
        }
        return ans;
    }
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        set<vector<int>> ans;
        for(int i =0 ;i < nums.size();i++){
            vector<vector<int> >x = threeSum(nums,(long long)target-nums[i],i+1);
            if(x.size()!=0){
                for(auto v:x){
                    v.push_back(nums[i]);
                    ans.insert(v);
                }
            }
        }
        vector<vector<int>> answer;
        for(auto v:ans){
            answer.push_back(v);
        }
        return answer;
    }
};
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