CodingHardcod-g896

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

Question

Count how many integers in the inclusive range [1, n] have the property that every pair of adjacent decimal digits differs by at least 2 (i.e. |d_i - d_{i+1}| >= 2 for all consecutive digits, reading the number with no leading zeros). Single-digit numbers trivially qualify since they have no adjacent pair. Return the count. 1 <= n <= 10^9.

Implement

count_diff_at_least_two(n: int) → int

Examples

in[20]out17

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.