<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) {
        int left=0;
        int right=1;
        sort(changed.begin(),changed.end());
        vector<int> f;
        if(changed.size()%2==1){
            return f;
        }
        int n=changed.size();
        f=vector<int>(n);
        vector<int> e;
        // int count=0;
        while(right<n and left<n){
            if(f[left]==1){
                left++;
                continue;
            }
            f[left]=1;
            right=max(right,left+1);
            // count++;
            while((right<n and changed[left]*2!=changed[right]) or (right<n and f[right]==1)){
                right++;
            }
            if(right<n){
                f[right]=1;
                // cout<<left<<" ";
                e.push_back(changed[left]);
                // count++;
            }
            else{
                break;
            }
        }
    // for(int i=0;i<e.size();i++){
    //     cout<<e[i]<<" ";
    // }
    if(e.size()==n/2) return e;
    else return vector<int>();

    
    }
};
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