[Swift]LeetCode357. 计算各个位数不同的数字个数 | Count Numbers with Unique Digits

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

Example:

Input: 2
Output: 91
Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100,
             excluding 11,22,33,44,55,66,77,88,99

示例:

输入: 2
输出: 91
解释: 答案应为除去 11,22,33,44,55,66,77,88,99 外，在 [0,100) 区间内的所有数字。

8ms

 1 class Solution {
 2     func countNumbersWithUniqueDigits(_ n: Int) -> Int {
 3         if n == 0 {return 1}
 4         if n == 1 {return 10}
 5         var res:Int = 10
 6         var cnt:Int = 9
 7         for i in 2...n
 8         {
 9             cnt *= (11 - i)
10             res += cnt
11         }
12         return res
13     }
14 }

1 class Solution {
2     func countNumbersWithUniqueDigits(_ n: Int) -> Int {
3         var nums = [1, 10, 91, 739, 5275, 32491, 168571, 712891, 2345851, 5611771, 8877691]
4         return nums[min(10, n)]
5     }
6 }

原文地址：https://www.cnblogs.com/strengthen/p/10276840.html