CodingHardcod-g267

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

Question

Return the sum of the decimal digits of every integer from 0 to n inclusive. For n=12 the answer is 0+1+2+...+9+1+(1+0)+(1+1)+(1+2) = 51. 0 <= n <= 10^12. Use an approach that does not iterate over every integer.

Implement

digit_sum_upto(n: int) → int

Examples

in[12]out51

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.