<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:
	int ret = 0;
	void foo(string tiles, int st, int n) {
		vector<bool> visited(26, false);
		if(st == n)
		{
			ret++;
		}else{
			for(int idx=st; idx<tiles.length(); idx++){
				if(visited[tiles[idx] - 'A'] == false){
					visited[tiles[idx] - 'A'] = true;
					swap(tiles[idx], tiles[st]);
					foo(tiles, st+1, n);
					swap(tiles[idx], tiles[st]);
				}
			}
		}
    }
    int numTilePossibilities(string tiles) {
        for(int i=1; i<=tiles.length(); i++)
        {
            foo(tiles, 0, i);
        }
		return ret;
    }
};
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