<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) {
        // Sort list for reliable dupe skipping
        std::sort(nums.begin(), nums.end());
        set<vector<int>> set;
        vector<vector<int>> output;
        int len = nums.size();

        for(int D = len - 1; D >= 3; D--)
        {
            int dVal = nums[D];

            if(D > 6)
            {
                int dNext = nums[D - 4];
                if(dNext == dVal)
                {
                    continue;
                }
            }

            for(int A = 0; A + 2 < D; A++)
            {

                int B = A + 1;
                int C = D - 1;

                int aVal = nums[A];
                int bVal = nums[B];
                int cVal = nums[C];

                int aNxt = nums[A + 3];

                if(aVal == aNxt && A + 3 < D)
                {
                    continue;
                }

                while(B < C)
                {
                    bVal = nums[B];
                    cVal = nums[C];
                    long sum = 0;
                    sum += aVal;
                    sum += bVal;
                    sum += cVal;
                    sum += dVal;
                    vector<int> tempVec = { aVal, bVal, cVal, dVal };

                    if(sum <= target)
                    {
                        if(B != A + 1 && bVal == nums[B - 1])
                        {
                            B++;
                            continue;
                        }
                        else
                        {
                            B++;
                        }
                        if(sum == target && set.find(tempVec) == set.end())
                        {
                            set.insert(tempVec);
                            output.push_back(tempVec);
                        }
                    }

                    else
                    {
                        if(C != D - 1 && cVal == nums[C + 1])
                        {
                            C--;
                            continue;
                        }
                        else
                        {
                            C--;
                        }
                    }
                }
            }
        }
        return output;
    }

    void printVector(const std::vector<int>& vec) {
        for (int value : vec) {
            std::cout << value << " ";
        }
        std::cout << std::endl;
    }
};
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