Count unique digits one liner (efficiently)
<p>I'm searching for a way to count unique digits efficiently with a one liner.</p>

<p>For example: given the integer <code>623562</code>, return value would be <code>4</code>.</p>

<p>My current way of doing it is, given integer <code>i</code>, im using <code>len(set(str(i)))</code>.
Creating a set is time consuming. I'm going over alot of numbers so I need an efficient way.</p>

<p>Also, if someone can find a way to go over all the numbers with <code>x</code> digits without using
<code>range()</code> (and in a one liner..), I'll be glad. Memory limits me when using <code>range</code> because a list is created (I assume).</p>
