357 - Count Numbers With Unique Digits
Written on November 7, 2017
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Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.
class Solution(object):
def countNumbersWithUniqueDigits(self, n):
"""
:type n: int
:rtype: int
"""
if n == 0:
return 1
ret = 10
available_number = 9
unique_digit = 9
while n > 1:
unique_digit *= available_number
ret += unique_digit
n -= 1
available_number -= 1
return ret