<p>Write a method to compute all permutations of a string whose characters are not necessarily unique. The list of permutations should not have duplicates.</p>



<p><strong>Example1:</strong></p>



<pre>

<strong> Input</strong>: S = &quot;qqe&quot;

<strong> Output</strong>: [&quot;eqq&quot;,&quot;qeq&quot;,&quot;qqe&quot;]

</pre>



<p><strong>Example2:</strong></p>



<pre>

<strong> Input</strong>: S = &quot;ab&quot;

<strong> Output</strong>: [&quot;ab&quot;, &quot;ba&quot;]

</pre>



<p><strong>Note:</strong></p>



<ol>

	<li>All characters are English letters.</li>

	<li><code>1 &lt;= S.length &lt;= 9</code></li>

</ol>