<p>We call a positive integer <strong>special</strong> if all of its digits are <strong>distinct</strong>.</p>

<p>Given a <strong>positive</strong> integer <code>n</code>, return <em>the number of special integers that belong to the interval </em><code>[1, n]</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 20
<strong>Output:</strong> 19
<strong>Explanation:</strong> All the integers from 1 to 20, except 11, are special. Thus, there are 19 special integers.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 5
<strong>Output:</strong> 5
<strong>Explanation:</strong> All the integers from 1 to 5 are special.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> n = 135
<strong>Output:</strong> 110
<strong>Explanation:</strong> There are 110 integers from 1 to 135 that are special.
Some of the integers that are not special are: 22, 114, and 131.</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 2 * 10<sup>9</sup></code></li>
</ul>

class Solution:
    def countSpecialNumbers(self, n: int) -> int:
        
        digits = [int(i) for i in str(n)]
        usedDigits = set()
        l = len(digits)

        totalCount = 0
        if l >= 2:
            temp = 1
            for i in range(l-2):
                temp *= 9-i
                totalCount +=temp
            totalCount *= 9
            totalCount+=9
        nUsed = 0
        stop = False
        for i in range(l):
            d = digits[i]
            count = -1 if i == 0 else 0
            for d1 in range(d):
                if d1 not in usedDigits:
                    count +=1
            nUsed +=1
            for j in range(l-i-1):
                count *= (10-nUsed-j)
            totalCount += count
            if d not in usedDigits:
                usedDigits.add(d)
            else:
                stop=True
                break
            
        
        if digits[-1] not in digits[:-1] and not stop:
            totalCount+=1
        
        return totalCount
            
30