CodingHardcod-g483

Subject Digit dpLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Count integers n in [1, N] whose decimal representation has no two adjacent equal digits (e.g. 121 is fine, 122 is not). N can be up to about 10^15. Leading zeros are not part of the number, so the constraint applies only to actual digits.

Implement

count_no_adjacent_equal(N: int) → int

Examples

in[20]out19

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.