<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) {

        /* question says order is not important but the API says order is important. thats why this line: */
   

        std::vector<std::vector<int>> result;
        std::map<std::string,std::vector<int>> r;
        
        /* remove duplicates for optimization */
        std::map<int,int> tmp;
        for(auto e:nums)
        {
    
            tmp[e]++;
        }
       

        std::vector<int> nums2;
        
        for(auto e:tmp)
        {
            if(e.second == 1)
                nums2.push_back(e.first);
            else if(e.second == 2)
            {
                nums2.push_back(e.first);            
                nums2.push_back(e.first);            
            }
            else if(e.second > 2)
            {
                nums2.push_back(e.first);            
                nums2.push_back(e.first);        
                nums2.push_back(e.first);            
            }
        }
        nums = nums2;
        const int n = nums.size();

        std::map<int,bool> cache1;
        for(int i=0;i<n;i++)
            cache1[nums[i]]=true;
        std::map<int,std::vector<std::vector<int>>> cache2;
        for(int i=0;i<n;i++)
            for(int j=0;j<n;j++)
            {
                if(i!=j && cache1.find(-nums[i]-nums[j]) != cache1.end())
                {
                    if(cache2.find(-nums[i]-nums[j])==cache2.end())
                    {
                        cache2[-nums[i]-nums[j]]={{i,j}};
                    }
                    else
                    {
                        cache2[-nums[i]-nums[j]].push_back({i,j});
                    }
                }
            }

        for(int i=0;i<n;i++)
        {
            if(cache2.find(nums[i])!=cache2.end())
            {
                auto index = cache2[nums[i]];
                for(auto e:index)
                {
                    if(e[0] == i || e[1] == i) continue;
                    
                    int tmp[3]={nums[e[0]],nums[e[1]],nums[i]};
                    std::sort(tmp,tmp+3);
                    r[
                        std::to_string(tmp[0])+"_"+
                        std::to_string(tmp[1])+"_"+
                        std::to_string(tmp[2])
                    ]=
                    {
                        tmp[0],
                        tmp[1],
                        tmp[2]
                    };
                }
            }
        }

        for(auto e:r)
            result.push_back(e.second);
        return result;
    }
};
287551