CodingHardcod-g711

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

Question

Count how many integers x in the inclusive range [lo, hi] have a digit sum that is divisible by a given modulus k. Return the count. Constraints: 0 <= lo <= hi <= 10**18, 1 <= k <= 100. A brute-force loop over the range is far too slow; use digit DP with a prefix-count(hi) - prefix-count(lo-1) approach.

Implement

count_digit_sum_divisible(lo: int, hi: int, k: int) → int

Examples

in[1,20,3]out6

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.