<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 g(int ind, string &A, unordered_map<string,int> &m, string &t){
        if(ind==A.size()){
            if(t.size()) m[t]++;
            return;
        }
        g(ind+1, A, m, t);
        t.push_back(A[ind]);
        g(ind+1, A, m, t);
        t.pop_back();
    }
    void f(int ind, string &A, unordered_map<string,int> &m){
        if(ind==A.size()) {
            string t="";
            g(0, A, m, t);
            return ;
        }
        for(int i=ind+1;i<A.size();i++){
            swap(A[i], A[ind]);
            f(ind+1, A, m);
            swap(A[i], A[ind]);
        }
        f(ind+1, A, m);
    }
    int numTilePossibilities(string A) {
        unordered_map<string,int> m;
        f(0, A, m);
        return m.size();
    }
};
22044