Leetcode•Aug 08, 2025
Count Numbers with Unique Digits
Hazrat Ali
Leetcode
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
Solution
/**
* @param {number} n
* @return {number}
*/
const countNumbersWithUniqueDigits = n => {
if (n === 0) {
return 1;
}
let count = 10;
let unique = 9;
let ok = 9;
while (n-- > 1 && ok > 0) {
unique = unique * ok;
count += unique;
ok--;
}
return count;
};