<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:
  bool rep(string s) {
        unordered_set<char>cs;
        for(char c:s) {
            if(cs.find(c)!=cs.end()) {
                return true;
            }
            cs.insert(c);
        }
        return false;
    }
bool check(string a,string s1)
{
    unordered_map<char,int>mp;
    for(int i=0;i<s1.length();i++)
    {
        mp[s1[i]]++;
    }
    for(int i=0;i<a.length();i++)
    {
        if(mp.find(a[i])!=mp.end())
        {
            return false;
        }
    }
    return true;
}
int solve(vector<string>&arr,int i,string s,vector<int>&t)
{
    if(i==arr.size())
    {
        return t[i]=s.length();
    }
    int len=s.length();
    if(!rep(arr[i])&&check(arr[i],s))
    {
        t[i]=solve(arr,i+1,s+arr[i],t);
        len=max(len,t[i]);
    }
        t[i]=solve(arr,i+1,s,t);
        len=max(len,t[i]);
    return t[i]=len;
}
    int maxLength(vector<string>& arr){
        vector<int>t(17,-1);
        return solve(arr,0,"",t);
    }
};
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