CodingMediumcod-g801

Subject CombinatoricsLevel Mid–Senior~20 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given an integer `k`, count how many non-negative integers x with 0 <= x < 10^k have all distinct digits. For k = 0 the range is just {0}, so the answer is 1. 0 <= k <= 9.

Implement

count_numbers_with_unique_digits(k: int) → int

Examples

in[2]out91

What a strong answer looks like

State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.

Learn the concepts

Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.

Run or narrate your approach, then ask the coach.