leetcode 357. Count Numbers with Unique Digits

冷不防 2022-09-21 13:22 143阅读 0赞

Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.

Example:
Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x < 100, excluding [11,22,33,44,55,66,77,88,99])

  1. def fac(m):
  2.         if m==0 or m==1:
  3.             return 1
  4.         return fac(m-1)*m
  5. class Solution(object):
  6.     def __init__(self):
  7.         self.lookup=[]
  8.         self.lookup.append(10)
  9.         for i in xrange(2,10):
  10.             self.lookup.append(fac(9)/fac(10-i)*(i-1)+fac(9)/fac(9-i))
  12.     def countNumbersWithUniqueDigits(self, n):
  13.         """
  14.         :type n: int
  15.         :rtype: int
  16.         """
  17.         if n>9:
  18.             return sum(self.lookup)
  19.         if n:
  20.             return sum(self.lookup[0:n])
  21.         return 1

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