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Group Anagrams at Stripe — Interview Guide

How to approach Group Anagrams in a Stripe interview: the optimal approach, what Stripe interviewers look for, and company-specific tips.

Updated 2026-09MediumArrays & Hashing

The problem at Stripe

Given an array of strings, group the anagrams together. An anagram group contains strings that are rearrangements of the same letters.

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

Sorting each string gives a canonical key — O(k log k) per string.
A 26-character count tuple is a key in O(k) per string and is faster for long strings.
Both produce the same groups; the count key wins when strings are long.

Approach

import collections
def group_anagrams(strs):
    groups = collections.defaultdict(list)
    for s in strs:
        key = [0] * 26
        for c in s:
            key[ord(c) - 97] += 1
        groups[tuple(key)].append(s)
    return list(groups.values())

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.

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