<p>Given an integer array nums, return all the triplets <code>[nums[i], nums[j], nums[k]]</code> such that <code>i != j</code>, <code>i != k</code>, and <code>j != k</code>, and <code>nums[i] + nums[j] + nums[k] == 0</code>.</p>

<p>Notice that the solution set must not contain duplicate triplets.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [-1,0,1,2,-1,-4]
<strong>Output:</strong> [[-1,-1,2],[-1,0,1]]
<strong>Explanation:</strong> 
nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0.
nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0.
nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0.
The distinct triplets are [-1,0,1] and [-1,-1,2].
Notice that the order of the output and the order of the triplets does not matter.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,1,1]
<strong>Output:</strong> []
<strong>Explanation:</strong> The only possible triplet does not sum up to 0.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,0,0]
<strong>Output:</strong> [[0,0,0]]
<strong>Explanation:</strong> The only possible triplet sums up to 0.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>3 &lt;= nums.length &lt;= 3000</code></li>
	<li><code>-10<sup>5</sup> &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        // num -> indexes
        unordered_map<int, vector<int>> indexes;
        sort(nums.begin(), nums.end());

        for (auto i = 0; i < nums.size(); ++i) {
            indexes[nums[i]].push_back(i);
        }

        vector<vector<int>> result;
        unordered_set<string> result_strings;

        int prev_i = std::numeric_limits<int>::min();
        for (int i = 0; i < nums.size(); ++i) {

            if (nums[i] == prev_i) continue;
            else prev_i = nums[i];

            int prev_ii = std::numeric_limits<int>::min();
            for (int ii = i + 1; ii < nums.size(); ++ii) {

                if (nums[ii] == prev_ii) continue;
                else prev_ii = nums[ii];

                int rest = 0 - nums[i] - nums[ii];

                int prev_ind = -1;
                for (auto ind : indexes[rest]) {

                    if (ind <= i || ind <= ii) continue;

                    if (prev_ind != -1 && nums[ind] == nums[prev_ind]) continue;
                    else prev_ind = ind;

                    vector<int> candidate = {nums[i], nums[ii], nums[ind]};
                    result.push_back(candidate);
                }
            }
        }

        return result;
    }

    bool is_duplicate(vector<int>& candidate, unordered_set<string>& result_strings) {
        sort(candidate.begin(), candidate.end());
        string str;
        char delim = ',';
        for (auto el : candidate) {
            str += (std::to_string(el));
            str.push_back(delim);
        }
        if (result_strings.contains(str)) return true;
        else {
            result_strings.insert(str);
            return false;
        }
    }

};
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