<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> st;
    void subs(string s, int i, string temp) {
        if (i >= s.length()) {
            st.insert(temp);
            return;
        }
        subs(s, i + 1, temp);
        temp += s[i];
        subs(s, i + 1, temp);
    }
    void perm(string tiles, int i) {
        if (i == tiles.size() - 1) {
            subs(tiles, 0, "");
            return;
        }
        for (int j = i; j < tiles.size(); j++) {
            swap(tiles[j], tiles[i]);
            perm(tiles, i + 1);
            swap(tiles[j], tiles[i]);
        }
    }
    int numTilePossibilities(string tiles) {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout.tie(nullptr);
        perm(tiles, 0);
        return st.size() - 1;
    }
};
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