Carry the One

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant grading.

Domain

Python

Difficulty

medium

Seniority

mid

Problem

We store counters too big for 64 bits as arrays of base-1,000,000,000 limbs, least significant limb first. Subtracting `b` from `a` (with `a` never smaller than `b`) the way you would on paper, some columns force a borrow from the next limb up. Return the limb indices where a borrow is taken, lowest first.

Summary

In grade-school subtraction you scribble a mark each time you borrow. Recover those marks.

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