CodingMediumcod-g792

Subject CombinatoricsLevel Mid–Senior~25 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given a string `tiles` of uppercase letters (possibly with duplicates), return the number of distinct non-empty sequences you can form using the tiles, where each tile may be used at most once. For example with tiles `AAB`, sequences include `A`, `B`, `AA`, `AB`, `BA`, `AAB`, `ABA`, `BAA`. The string has length 1..10.

Implement

num_tile_possibilities(tiles: str) → int

Examples

in["AAB"]out8

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.