<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:
    map<string,bool> m;
    int fact(int n) {
        if (n == 0)
            return 1;
        if (n<= 2)
            return n;
        return n*fact(n-1);
    }
    int numTilePossibilities(string tiles) {
        if (m.find(tiles) != m.end())
            return 0;
        m[tiles] = true;
        if (tiles.size() == 1)
            return 1;
        vector<int> data(26,0);
        for (int i=0;i<tiles.size();i++)
            data[tiles[i]-'A']++;
        int ans = fact(tiles.size());
        for (int i=0;i<26;i++)
            ans /= fact(data[i]);

        int sum = 0;
        sort(tiles.begin(),tiles.end());
        sum += numTilePossibilities(tiles.substr(1,tiles.size()-1));
        for (int i=1;i<tiles.size();i++)
        {
            if (tiles[i] != tiles[i-1])
                sum += numTilePossibilities(tiles.substr(0,i)+tiles.substr(i+1,tiles.size()-i-1));
        }
        
        return sum+ans;

    }
};
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