CodingHardcod-g259

Subject Digit dpLevel Senior–Staff~35 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given a non-negative integer n, count how many integers x with 0 <= x <= n have NO two adjacent digits equal in their usual base-10 representation (e.g. 11 and 122 are invalid; 121 and 5 are valid; single-digit numbers including 0 are valid). 0 <= n <= 10^9. Return the count.

Implement

count_no_adjacent_equal(n: int) → int

Examples

in[22]out21

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.