Count Numbers with Unique Digits

Problem: Count Numbers with Unique Digits

Follow hint 4.

Code in Python:

class Solution(object):
    def countNumbersWithUniqueDigits(self, n):
        """
        :type n: int
        :rtype: int
        """
        def compF(k):
            if k == 0: return 1
            res = 9
            cur = 10
            while cur != 11-k:
                cur -= 1
                res *= cur
            return res

        res = 0
        for k in xrange(min(n+1, 10)):
            res += compF(k)
        return res