<p>An integer array <code>original</code> is transformed into a <strong>doubled</strong> array <code>changed</code> by appending <strong>twice the value</strong> of every element in <code>original</code>, and then randomly <strong>shuffling</strong> the resulting array.</p>

<p>Given an array <code>changed</code>, return <code>original</code><em> if </em><code>changed</code><em> is a <strong>doubled</strong> array. If </em><code>changed</code><em> is not a <strong>doubled</strong> array, return an empty array. The elements in</em> <code>original</code> <em>may be returned in <strong>any</strong> order</em>.</p>

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

<pre>
<strong>Input:</strong> changed = [1,3,4,2,6,8]
<strong>Output:</strong> [1,3,4]
<strong>Explanation:</strong> One possible original array could be [1,3,4]:
- Twice the value of 1 is 1 * 2 = 2.
- Twice the value of 3 is 3 * 2 = 6.
- Twice the value of 4 is 4 * 2 = 8.
Other original arrays could be [4,3,1] or [3,1,4].
</pre>

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

<pre>
<strong>Input:</strong> changed = [6,3,0,1]
<strong>Output:</strong> []
<strong>Explanation:</strong> changed is not a doubled array.
</pre>

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

<pre>
<strong>Input:</strong> changed = [1]
<strong>Output:</strong> []
<strong>Explanation:</strong> changed is not a doubled array.
</pre>

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

<ul>
	<li><code>1 &lt;= changed.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= changed[i] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    vector<int> findOriginalArray(vector<int>& changed) {
        // if(changed=={1,2,1,0}) return {};
        unordered_map<int,vector<int>> mpp;
        int cnt=0;
        int n=changed.size();
        if(n&1) return {};
        sort(changed.begin(),changed.end());
        vector<int> visited(n,0);
        for(int i=0;i<n;i++){
            if(changed[i]==0) cnt++;
            else mpp[changed[i]].push_back(i);
        }
        vector<int> ans;
        if(cnt%2==0){
            for(int i=0;i<cnt/2;i++) ans.push_back(0);
        }
        for(int i=0;i<n;i++){
            int num=changed[i];
            if(num!=0){
            if(visited[i]==0){
            if(mpp.find(num*2)!=mpp.end()){
                vector<int> temp=mpp[num*2];
                int i=0;
                int flag=0;
                while(i<temp.size()){
                    if(visited[mpp[num*2][i]]==0){
                        visited[mpp[num*2][i]]=1;
                        ans.push_back(num);
                        flag=1;
                        break;
                    }
                    i++;
                }
                if(flag==0) return {};
            }
            else{
                return {};
            }
            visited[i]=1;
            }
        }
        }
        return ans;
    }
};
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