Code Room
CodingHardcod-g832
Subject Bit manipulationLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Return the total number of set bits (1-bits) across the binary representations of all integers from 0 to n inclusive, for n up to 10^9. Iterating each number and calling popcount is too slow; instead count bit position by bit position. For bit position i, the i-th bit cycles with period 2^(i+1): it is 0 for the first 2^i numbers and 1 for the next 2^i. Sum the contributions. Return 0 for n < 0.

Implement
count_set_bits_range(n: int) → int
Examples
in[5]out7
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.

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.