如何不重复计数渐近数

def countDistinctAsymptoticNumbers(maxDigits):
    def isAsymptoticNumber(num, prevDigit):
        if prevDigit is None:
            return True
        return num > prevDigit or num < prevDigit

    def countDistinctAsymptoticNumbersRec(num, digit, prevDigit, usedDigits):
        if digit == maxDigits:
            return 1

        count = 0
        for i in range(10):
            if i in usedDigits:
                continue
            if isAsymptoticNumber(i, prevDigit):
                usedDigits.add(i)
                count += countDistinctAsymptoticNumbersRec(num * 10 + i, digit + 1, i, usedDigits)
                usedDigits.remove(i)

        return count

    return countDistinctAsymptoticNumbersRec(0, 0, None, set())

maxDigits = 3
result = countDistinctAsymptoticNumbers(maxDigits)
print("不重复计数渐近数的个数为:", result)