<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:
    int n;
    bool hasUniqueCharacters(const string& s) {
        unordered_map<char, int> charCount;
        for (char ch : s) {
            if (++charCount[ch] > 1) return false;
        }
        return true;
    }
    bool comapare(string s1,string s2){
        if(s1.length() == 0) return true;

        unordered_map<char,int>mpp;
        for(auto ch : s1){
            mpp[ch]++;
        }
        for(auto ch : s2){
            mpp[ch]++;
        }
        for(auto it : mpp){
            if(it.second == 2) return false;
        }
        return true;

    }
    int f(int i,vector<string>& arr,string &s){
        if(i == n) return 0;

        
        // not take 
        int not_take = 0 + f(i+1,arr,s);
        int take  = 0 ;
        // take 
        if(comapare(arr[i],s) && hasUniqueCharacters(arr[i])){
            s += arr[i];
            take = arr[i].length() + f(i+1,arr,s);
            s.erase(s.length() - arr[i].length(), arr[i].length());
        }
        
        return max(take,not_take);
    }
    int maxLength(vector<string>& arr) {
        n = arr.size();
        string s = "";
        return f(0,arr,s);
    }
};
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