<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) {
        int n = nums.size();
        set<vector<int>>st;
        vector<vector<int>>ans;
        long long sum = 0;
        // Approach1
        // for(int i=0;i<n;i++){
        //     for(int j=i+1;j<n;j++){
        //         for(int k=j+1;k<n;k++){
        //             for(int l=k+1;l<n;l++){
        //                 sum = (long long)((long long)nums[i]+(long long)nums[j]+(long long)nums[k]+(long long)nums[l]);
        //                 if(sum==(long long)target){
        //                     vector<int>temp;
        //                     temp.push_back(nums[i]);
        //                     temp.push_back(nums[j]);
        //                     temp.push_back(nums[k]);
        //                     temp.push_back(nums[l]);
        //                     sort(temp.begin(), temp.end());
        //                     st.insert(temp);
        //                 }
        //             }
        //         }
        //     }
        // }
        // for(auto i:st){
        //     ans.push_back(i);
        // }

        // Approach2
        sort(nums.begin(), nums.end());
        map<long long,long long>mp;
        for(int i=0;i<n;i++){
            mp[nums[i]]++;
        }
        for(int i=0;i<n;i++){
            mp[nums[i]]--;
            for(int j=i+1;j<n;j++){
                mp[nums[j]]--;
                for(int k=j+1;k<n;k++){
                    mp[nums[k]]--;
                    sum = (long long)((long long)nums[i]+(long long)nums[j]+(long long)nums[k]);
                    long long x = target-sum;
                    if(mp[target-sum]>0){
                        vector<int>temp(4);
                        if(x<nums[i]){
                            temp[0] = x;
                            temp[1] = nums[i];
                            temp[2] = nums[j];
                            temp[3] = nums[k];
                        }
                        else if(x<nums[j]){
                            temp[1] = x;
                            temp[0] = nums[i];
                            temp[2] = nums[j];
                            temp[3] = nums[k];
                        }
                        else if(x<nums[k]){
                            temp[2] = x;
                            temp[0] = nums[i];
                            temp[1] = nums[j];
                            temp[3] = nums[k];
                        }
                        else{
                            temp[3] = x;
                            temp[0] = nums[i];
                            temp[1] = nums[j];
                            temp[2] = nums[k];
                        }
                        st.insert(temp);
                }
                mp[nums[k]]++;   
                 }
            mp[nums[j]]++;
            }
        }
        for(auto i:st){
            ans.push_back(i);
        }
        return ans;
    }
};
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