LeetCode-in-Java
357. Count Numbers with Unique Digits
Medium
Given an integer n, return the count of all numbers with unique digits, x, where 0 <= x < 10n.
Example 1:
Input: n = 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
Example 2:
Input: n = 0
Output: 1
Constraints:
0 <= n <= 8
Solution
public class Solution {
public int countNumbersWithUniqueDigits(int n) {
int ans = 1;
for (int i = 1; i <= n; i++) {
int mul = 1;
for (int j = 1; j < i; j++) {
mul *= (10 - j);
}
ans = ans + 9 * mul;
}
return ans;
}
}