<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) {
    int n = nums.size();
    sort(nums.begin(), nums.end());

    set<multiset<int>> st;
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            long long curr = target - long(nums[i] + nums[j]);
            int low = j+1, high = n-1;
            while(low<high){
                if(long(nums[low]) + long(nums[high]) == curr){
                    multiset<int> mul_st;
                    mul_st.insert(nums[i]);
                    mul_st.insert(nums[j]);
                    mul_st.insert(nums[low]);
                    mul_st.insert(nums[high]);
                    st.insert(mul_st);
                    low++; high--;
                }
                else if(nums[low] + nums[high] < curr){
                    low++;
                }
                else{
                    high--;
                }
            }
        }
    }

    vector<vector<int>> ans;
    for(auto& sum : st){
        vector<int> temp;
        for(auto& num : sum){
            temp.push_back(num);
        }
        ans.push_back(temp);
    }
    return ans;
}
};
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