<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 all_combo(string tiles, int idx, string curr, unordered_set<string>& st){
        if(idx>=tiles.size()){
            if(curr!="")
            st.insert(curr);
            return;
        }
        all_combo(tiles, idx+1, curr+tiles[idx], st);
        all_combo(tiles, idx+1, curr, st);
    }
    map<int,int> fact_table;
    int fact(int n){
        if(n==0 || n==1)return 1;
        if(fact_table[n])return fact_table[n];
        int ans = fact(n-1)*n;
        fact_table[n] = ans;
        return ans;
    }
    int numTilePossibilities(string tiles) {
        sort(tiles.begin(),tiles.end());
        unordered_set<string> st;
        all_combo(tiles, 0, "", st);
        int ans = 0;
        for(auto i: st){
            vector<int> cnt(26,0);
            int div=1;
            for(auto j: i){
                cnt[j-'A']++;
            }
            for(int k=0;k<26;++k){
                if(cnt[k]){
                    div=div*fact(cnt[k]);
                    
                }
            }
            ans += fact(i.size())/div;
        }
        return ans;
    }
};
 
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