<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
        std::sort(nums.begin(), nums.end(), std::less<>());
        //std::ranges::copy(nums, std::ostream_iterator<int>(std::cout, " "));
        //std::cout << "\n---------\n";
        // remove duplicates - we guarantee distinc values
        // nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
        // std::ranges::copy(nums, std::ostream_iterator<int>(std::cout, " "));
        // std::cout << "\n---------\n";
        std::vector<std::vector<int>> output;

        auto n = nums.size();
        if(n < 4)
            return {};

        for (int i = 0; i < n - 3; ++i) {
            for (int j = i+1; j < n - 2; ++j) {
                auto left = j + 1;  // go forwards
                auto right = n - 1; // go back

                int64_t sub_target = (int64_t)target -  (int64_t)nums[i] - (int64_t)nums[j];
                // if(sub_target <= 0) cant do that, we need to assume other
                // values are negative
                //     continue; //
                while (left < right) {
                    auto l_r_sum = nums[left] + nums[right];
                    if (l_r_sum < sub_target) {
                        left++;
                    } else if (l_r_sum > sub_target) {
                        right--;
                    } else {
                        //std::cout <<"i="<<i <<"\tj="<<j<<"\tleft="<<left<<"\trigh="<<right<<std::endl;
                        std::vector<int> o{nums[i], nums[j], nums[left],
                                           nums[right]};
                        //std::ranges::copy(
                        //    o, std::ostream_iterator<int>(std::cout, " "));
                       // std::cout << "\n";
                        //std::sort(o.begin(), o.end(), std::less<>()); //we can skip sorting if we go i,j l,r
                        //std::cout << "after sorting\n";
                        //std::ranges::copy(
                        //    o, std::ostream_iterator<int>(std::cout, " "));
                        //std::cout << "\n";
                        output.emplace_back(std::move(o));
                        left++;
                        right--;
                    }
                }
            }
        }
        //std::cout << "output.size=" << output.size() <<std::endl;
        std::set<std::vector<int>> s{output.begin(), output.end()};
        //std::cout << "s.size=" << s.size() <<std::endl;
        output = std::vector<std::vector<int>>{s.begin(), s.end()};

        return output;
    }
};
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