<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 {
public:
unordered_map<char,bool> mp;
bool checks(string s){
    for(int j=0;j+1<s.length();j++){
            if(mp[s[j]]==true || s[j] == s[j+1]){
                return false;
            }
        }
        if(mp[s[s.length()-1]]){
            return false;
        }
        return true;
}
void solves(vector<string>& arr,int &maxi,int in,int l){
    if(in == arr.size()){
        maxi=max(maxi,l);
        return;
    }
    for(int i = in;i<arr.size();i++){
        string s=arr[i];
        sort(s.begin(),s.end());
        if(checks(s)){
            for(int j=0;j<s.length();j++){
                mp[s[j]]=true;
            }
            
            solves(arr,maxi,i+1,l+s.length());
            for(int j=0;j<s.length();j++){
                mp[s[j]]=false;
            }
        }
    }
     solves(arr,maxi,in+1,l);
     return;
}
    int maxLength(vector<string>& arr) {
        int maxi=0;
        solves(arr,maxi,0,0);
        return maxi;
    }
};
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