<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 canITake(string& first, string& second){
        set<char> st;
        set<char> ss;
        for(int i = 0; i < first.size(); i ++){
            if(st.find(first[i]) != st.end()) return false;
            st.insert(first[i]);
        }
        for(int i = 0; i < second.size(); i ++){
            if(ss.find(second[i]) != ss.end()) return false;
            ss.insert(second[i]);
        }
        for(char b : second){
            if(st.find(b) != st.end()){
                return false;
            }
        }
        return true;
    }
    int f(int index, string& currString, vector<string>& arr){
        int n = arr.size();
        if(index == n){
            // cout << currString << endl;
            return currString.size();
        }
        // Take and not Take
        string temp = currString;
        int take = 0;
        if(canITake(currString , arr[index])){
            currString += arr[index];
            take = f(index+1, currString, arr);
            currString = temp;
        }
        int notTake = f(index+1, currString, arr);
        cout << take << " " << notTake << endl;
        return max(take, notTake);
    }
    int maxLength(vector<string>& arr) {
        string currString = "";
        if(arr.size() == 1) {
            set<char> st;
            for(int i = 0; i < arr[0].size(); i ++){
                if(st.find(arr[0][i]) != st.end()) return 0;
                st.insert(arr[0][i]);
            }
            return arr[0].size();
        }
        return f(0, currString, arr);
    }
};
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