<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:
    unordered_set<string>s;
    void permute(std::string str, int l, int r, int k) {
        if (l == k) {
            s.insert(str.substr(0, k));
        } else {
            for (int i = l; i <= r; i++) {
                swap(str[l], str[i]);
                permute(str, l + 1, r, k);
                swap(str[l], str[i]);
            }
        }
    }
    int findTotal(int size, string tiles){
        s.clear();
        permute(tiles,0,tiles.size()-1,size);
        return s.size();
    }
    int numTilePossibilities(string tiles) {
        int ans=0;
        for(int i=1;i<tiles.size()+1;i++){
            ans+=findTotal(i,tiles);
        }
        return ans;
    }
};
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