<p>You have <code>n</code>&nbsp;&nbsp;<code>tiles</code>, where each tile has one letter <code>tiles[i]</code> printed on it.</p>

<p>Return <em>the number of possible non-empty sequences of letters</em> you can make using the letters printed on those <code>tiles</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> tiles = &quot;AAB&quot;
<strong>Output:</strong> 8
<strong>Explanation: </strong>The possible sequences are &quot;A&quot;, &quot;B&quot;, &quot;AA&quot;, &quot;AB&quot;, &quot;BA&quot;, &quot;AAB&quot;, &quot;ABA&quot;, &quot;BAA&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> tiles = &quot;AAABBC&quot;
<strong>Output:</strong> 188
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> tiles = &quot;V&quot;
<strong>Output:</strong> 1
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= tiles.length &lt;= 7</code></li>
	<li><code>tiles</code> consists of uppercase English letters.</li>
</ul>

// #include <iostream>
// #include <algorithm>
// #include <unordered_set>

// using namespace std;

// class Solution {
// public:
   

//     void help(string &s, int index, unordered_set<string> &uniqueSequences) {
//         if (index == s.size()) {
//             return;
//         }

//         for (int i = index; i < s.size(); i++) {
//             if (i > index && s[i] == s[i - 1]) {
//                 continue;  
//             }

//             swap(s[index], s[i]); 
//             uniqueSequences.insert(s.substr(0, index + 1));  // index , length 

//             help(s, index + 1, uniqueSequences); 
//             swap(s[index], s[i]); 
//         }
//     }

//     int numTilePossibilities(string tiles) {
//         sort(tiles.begin(), tiles.end());
//         unordered_set<string> uniqueSequences;
//         help(tiles, 0, uniqueSequences);
//         return uniqueSequences.size();
//     }
// };




class Solution 
{
  void recursion(string &tiles, unordered_map<int, bool> &visited, unordered_map<string, bool> &s, string temp)
    {
	    if(temp.size()==tiles.size())
		    return;

        for(int i=0; i<tiles.size(); i++)
		{
			if(!visited[i])
			{
				visited[i]=true;
				temp.push_back(tiles[i]);
				if(!s[temp])
				{
                    s[temp]=true;
					recursion(tiles, visited, s, temp);
					// s[temp]=true;  no effect 
				}
        //Backtrack 
				temp.pop_back();
				visited[i]=false;
			}
		}
	}
public:
  int numTilePossibilities(string tiles) 
	{
    
		unordered_map<int, bool> visited;
		unordered_map<string, bool> s;
        string temp="";
		recursion(tiles, visited, s,temp);
		return s.size();
    }
};
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