CodingHardcod-g178

Subject Modular arithmeticLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given integers a and m (1 <= a < m <= 10^9), return the modular multiplicative inverse of a modulo m — the integer x in [0, m) such that (a * x) % m == 1. If no inverse exists (because a and m are not coprime), return -1. Do not assume m is prime.

Implement

mod_inverse(a: int, m: int) → int

Examples

in[3,11]out4

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.