<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>

class Solution {
public:
    void solve(string tiles,set<string>&st,string&check,int i){
        if(i == tiles.size()){
            if(!check.empty()){
                st.insert(check);
            }
            return;
        }
        for(int j=i;j<tiles.size();j++){
            swap(tiles[i],tiles[j]);
            check+=tiles[i];
            solve(tiles,st,check,i+1);
            check.pop_back();
            solve(tiles,st,check,i+1);
            swap(tiles[i],tiles[j]);
        }
        
    }
    int numTilePossibilities(string tiles) {
        set<string>st;
        string check="";
        solve(tiles,st,check,0);
        return st.size();
    }
};
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