<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 {
private:
    bool equals(vector<int> a, vector<int> b) {
        for(int i=0; i<min(a.size(), b.size()); i++) {
            if(a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        if(nums.size() < 4) {
            return {};
        }
        vector<vector<int>> res;
        sort(nums.begin(), nums.end());

        for(int i=0; i<nums.size()-3; i++) {
            for(int j=i+1; j<nums.size()-2; j++) {
                int k = j+1, l = nums.size()-1;

                while(k < l) {
                    long sum = long(nums[i]) + long(nums[j]) + long(nums[k]) + long(nums[l]);
                    vector<int> temp = {nums[i], nums[j], nums[k], nums[l]};  
                     
                    if(sum < target) {
                        k++;
                    } else if(sum > target){
                        l--;
                    } else {
                        if(find(res.begin(),res.end(),temp)==res.end()) {
                            res.push_back(temp);
                        }
                        k++;
                        l--;
                    }
                }
            }
        }

        return res;
    }
};
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