<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:

    // check two string do not share any character
    bool checkUnique(string first, string second)
    {
        map<char, bool> mp;
        for(char val : first)
        {
            if(mp.find(val) != mp.end()) return false;
            mp[val] = true;
        }
        for(char val : second)
        {
            if(mp.find(val) != mp.end()) return false;
            mp[val] = true;
        }
        return true;
    }



    string maxString(vector<string>& arr, string currString, int idx)
    {
        if(idx >= arr.size()) return currString;
        string secondString = "";
        string firstString ="";
        cout << currString << endl;

        // without include current index string
        firstString = maxString(arr, currString , idx+1);

        // include current index string
        if(checkUnique(arr[idx], currString))
        {
            secondString = maxString(arr, currString + arr[idx] , idx+1);
        }
        

        // return max length string
        if(firstString.length() > secondString.length())
        {
            return firstString;
        }

        return secondString;


    }


    int maxLength(vector<string>& arr) {

        // init
        int maxLength = 0;
        int n = arr.size();
        string s = "";





        // loop
        string maxS = maxString(arr, s, 0);

        return maxS.length(); 

        
    }
};
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