<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) {
        vector<vector<int>> res;
        if (nums.size() < 4) return 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 left = j+1;
                int right = nums.size()-1;
                while (left < right)
                {
                    long sum = (long) nums[i] + nums[j] + nums[left] + nums[right];
                    vector<int> tmp = {nums[i], nums[j], nums[left], nums[right]};
                    if (sum == target)
                    {
                        res.push_back(tmp);
                        while (left < right && nums[left] == tmp[2]) left += 1;
                        while (left < right && nums[right] == tmp[3]) right -= 1;
                    }
                    else if (sum > target)
                    {
                        right -= 1;
                    }
                    else left += 1;
                }
            }
        }
        sort(res.begin(), res.end());
        auto iter = unique(res.begin(), res.end());
        res.erase(iter, res.end());
        return res;
    }
};
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