Multiply Strings
A medium-tier problem at 42% community acceptance, tagged with Math, String, Simulation. Reported in interviews at Two Sigma and 13 others.
Multiply Strings is a deceptively simple problem that trips up 58% of candidates. You're given two numbers as strings and need to return their product as a string. No converting to integers. That constraint kills the obvious path and forces you to simulate grade-school multiplication by hand. Two Sigma, Meta, Amazon, Apple, and Microsoft all ask this. The trick isn't complex, but missing it in a live assessment costs you 20 minutes of thrashing. StealthCoder surfaces the simulation pattern instantly if you freeze.
Companies that ask "Multiply Strings"
Multiply Strings is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe trap is trying to parse the strings into native integers. That fails on very large numbers or restricted languages. Instead, you simulate elementary school multiplication: iterate both strings backward, multiply digit pairs, handle carries, and build the result. The math is trivial. The implementation requires careful index management and understanding how carries propagate across positions. Most candidates know the concept but botch the indexing or forget the carry logic mid-implementation. When you hit this live and can't recall the exact sequence, StealthCoder runs invisibly and hands you the working code. The topics are Math, String, and Simulation, and all three matter equally here.
Pattern tags
You know the problem.
Make sure you actually pass it.
Multiply Strings recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Multiply Strings interview FAQ
Is this problem actually asked at top companies?+
Yes. It appears in reports from Amazon, Microsoft, Apple, Meta, and Bloomberg. It's particularly common in initial phone screens where they want to see if you can code carefully without relying on built-in math libraries. Not a curveball.
What's the acceptance rate and why is it low?+
42% acceptance. The problem looks easy but punishes sloppy indexing and carry logic. Candidates often get partial credit for logic but fail edge cases like leading zeros, empty strings, or single-digit carries cascading. Off-by-one errors are the silent killer here.
Can I just convert to int, multiply, and convert back?+
Not in a real interview. That's the first thing they rule out. Some languages have arbitrary-precision integers, but the interviewer will ask you to implement it without them. The constraint forces you to prove you understand the math, not just syntax.
What's the hardest part of this problem?+
Managing the result array indices and carries. You're building digits from right to left while iterating two input strings backward. Getting the formula result_index = i + j + 1 wrong or forgetting to handle a carry that flows into a new digit costs you. Test edge cases: zero multiplied by anything, single digits, strings of different lengths.
How does this relate to the String and Math topics?+
String work is just iteration and indexing. Math is the carry logic and positional arithmetic. Simulation is doing the entire multiplication process step by step. You're not using a library. You're proving you can break a familiar operation into primitive steps and code it correctly.
Want the actual problem statement? View "Multiply Strings" on LeetCode →