What is Interview Forge?

Interview Forge helps you practice mock interviews, follow study plans, track career goals, review learning analytics, and prepare across 36 pages.

Product of Array Except Self at Stripe — Interview Guide

How to approach Product of Array Except Self in a Stripe interview: the optimal approach, what Stripe interviewers look for, and company-specific tips.

Updated 2026-09MediumPrefix / Postfix

The problem at Stripe

Given an array nums, return an array output such that output[i] equals the product of all elements except nums[i], without using division and in O(n).

Stripe uses this problem to assess apis, money, and pragmatic engineering. Expect Stripe-specific follow-ups that tie the solution back to production reasoning and the company's engineering bar.

Key concepts

output[i] = (product of everything left of i) × (product of everything right of i).
First pass left-to-right accumulates the running left product.
Second pass right-to-left multiplies in the running right product.

Approach

def product_except_self(nums):
    res = [1] * len(nums)
    left = 1
    for i in range(len(nums)):
        res[i] = left
        left *= nums[i]
    right = 1
    for i in range(len(nums) - 1, -1, -1):
        res[i] *= right
        right *= nums[i]
    return res

What Stripe looks for

Pragmatic engineering — code that works and is maintainable.
API and product thinking — design interfaces developers love.
User empathy — Stripe cares deeply about developer experience.
Clarity in writing and communication.

Unlock the full guide

Premium members get every DSA, system design, company and role interview guide — plus AI practice, mock interviews, and analytics.

Unlock with Premium