<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>> ans;
    unordered_set<string> unique;
    void helper(int i,int j,int left,int right,vector<int>& nums){
        //check if duplicate or not
        vector<int> temp = {nums[i],nums[j],nums[left],nums[right]};
        sort(temp.begin(),temp.end());
        string track = "";
        track += to_string(temp[0]) + "," + to_string(temp[1]) + "," + to_string(temp[2]) +  "," + to_string(temp[3]) + ",";
        if(unique.count(track)>0)return;
        else{
            unique.insert(track);
            ans.push_back(temp);
        }
    }
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        unordered_set<string> pairVisit;
        for(int i=0;i<nums.size();i++){
            for(int j=i+1;j<nums.size();j++){
                long long curr_target = static_cast<long long>(target) - nums[i] - nums[j];
                int left=0,right=nums.size()-1;
                while(left<right){
                    long long curr = static_cast<long long>(nums[left]) + nums[right];
                    if(left!=i && left!=j && right!=i && right!=j && curr==curr_target){
                        helper(i,j,left,right,nums);
                        left++;
                        right--;
                    }
                    else if(curr>curr_target){
                        right--;
                    }
                    else left++;
                }
            }
        }
        return ans;
    }
};
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