<p>You are given an array of strings <code>arr</code>. A string <code>s</code> is formed by the <strong>concatenation</strong> of a <strong>subsequence</strong> of <code>arr</code> that has <strong>unique characters</strong>.</p>

<p>Return <em>the <strong>maximum</strong> possible length</em> of <code>s</code>.</p>

<p>A <strong>subsequence</strong> is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.</p>

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

<pre>
<strong>Input:</strong> arr = [&quot;un&quot;,&quot;iq&quot;,&quot;ue&quot;]
<strong>Output:</strong> 4
<strong>Explanation:</strong> All the valid concatenations are:
- &quot;&quot;
- &quot;un&quot;
- &quot;iq&quot;
- &quot;ue&quot;
- &quot;uniq&quot; (&quot;un&quot; + &quot;iq&quot;)
- &quot;ique&quot; (&quot;iq&quot; + &quot;ue&quot;)
Maximum length is 4.
</pre>

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

<pre>
<strong>Input:</strong> arr = [&quot;cha&quot;,&quot;r&quot;,&quot;act&quot;,&quot;ers&quot;]
<strong>Output:</strong> 6
<strong>Explanation:</strong> Possible longest valid concatenations are &quot;chaers&quot; (&quot;cha&quot; + &quot;ers&quot;) and &quot;acters&quot; (&quot;act&quot; + &quot;ers&quot;).
</pre>

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

<pre>
<strong>Input:</strong> arr = [&quot;abcdefghijklmnopqrstuvwxyz&quot;]
<strong>Output:</strong> 26
<strong>Explanation:</strong> The only string in arr has all 26 characters.
</pre>

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

<ul>
	<li><code>1 &lt;= arr.length &lt;= 16</code></li>
	<li><code>1 &lt;= arr[i].length &lt;= 26</code></li>
	<li><code>arr[i]</code> contains only lowercase English letters.</li>
</ul>

class Solution {

    private:
    int maxSize=0;
public:
    
    bool hasUnique(string &s1,string &s2){

    vector<bool> hash(26,false);
        


        for(int i=0;i<s1.size();i++){
            if(hash[s1[i]-'a']) return false;
            hash[s1[i]-'a']=true;
        }
        for(int i=0;i<s2.size();i++){
            if(hash[s2[i]-'a']) return false;
            hash[s2[i]-'a']=true;
        }
        return true;
    }

    void concatanation(int index,int n,string temp,vector<string> &arr){
        if(index==n){
            int size=temp.size();
            maxSize=max(maxSize,size);
            return;
        }

        if(!hasUnique(temp,arr[index])){
            concatanation(index+1,n,temp,arr);
        }

        else{
            concatanation(index+1,n,temp+arr[index],arr);
            concatanation(index+1,n,temp,arr);
        }
    }
    int maxLength(vector<string>& arr) {
        string temp="";
        int n=arr.size();
        concatanation(0,n,temp,arr);
        return maxSize;
    }
};
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