Letter Combinations of a Phone Number: which companies ask it and how to practise

Letter Combinations of a Phone Number is a Medium problem that 37 companies are reported to ask. This page shows who, how often and how recently, what the question tests, and how to practise it out loud with an interviewer who asks follow-ups. We link to the original problem statement instead of copying it.

Which companies ask Letter Combinations of a Phone Number?

Public company lists attribute Letter Combinations of a Phone Number, a Medium problem, to 37 companies. The most frequent askers are Dropbox, Trexquant and Epic Systems. 9 reports are from the last six months. It mainly tests hash table, string and backtracking. Use this as a practice guide, not a promise.

Practise this kind of question aloud

Who asks Letter Combinations of a Phone Number

37 companies appear in the public lists for this question. By how often each is reported: Dropbox (very often), Trexquant (very often), Epic Systems (very often), DE Shaw (often), LinkedIn (often), Accenture (often), Flexport (often), Societe Generale (often), Tesla (often) and Amazon (often), and 27 more. 9 of them were reported in the last six months, LinkedIn, Amazon and Microsoft among them.

These are candidate reports collected in public lists, not statements from the companies. They are a good guide to what to practise and a poor guide to what you will be asked: interviewers change questions, and the same company asks different questions by team and level. Last reviewed 25 October 2026.

What Letter Combinations of a Phone Number tests

It is rated Medium, which is the level most interviews are built around: expect to talk through two approaches, pick one, code it cleanly, and answer a cross-question on an edge case or a change to the constraints.

A hash table trades memory for speed: remembering what you have seen turns a repeated search into a lookup. Interviewers want you to say that trade-off and the cost of collisions or a bad key.

String problems test careful index handling and knowing which characters you may assume. Say out loud whether the input is ASCII, whether case matters, and what an empty string should return.

Backtracking builds a candidate step by step and undoes a step when it fails. Say how you prune, because that is what separates the answer from brute force.

How to practise it

Do not just solve it silently. In a real interview you explain the approach before you code, write while you talk, and defend the solution to follow-ups. Set a timer, say the brute force and its cost first, then improve it, and finish by stating the time and space complexity and two edge cases you tested.

On giveinterview you can take this kind of question as a spoken interview: the AI interviewer opens with the problem, watches you code, asks cross-questions and ends with a scorecard. Your first 3 single-question interviews are free for life, every interview report is free, and a new account also gets 6 welcome credits.

Read the original statement here: https://leetcode.com/problems/letter-combinations-of-a-phone-number/ (opens the publisher's page). The statement is theirs; we do not reproduce it.

Questions to practise next

If you can solve Letter Combinations of a Phone Number, try these next, chosen because they share its main topic and many of the same companies: Two Sum (Easy), LRU Cache (Medium), Longest Substring Without Repeating Characters (Medium), Group Anagrams (Medium), Top K Frequent Elements (Medium) and Subarray Sum Equals K (Medium). Each has its own page in the questions list.

Frequently asked questions

Is Letter Combinations of a Phone Number asked at Amazon?

Amazon appears in the public lists for Letter Combinations of a Phone Number, reported often. Treat that as a reason to practise it, not a promise you will be asked it.

How hard is Letter Combinations of a Phone Number?

Do I need to memorise the solution?

No. Interviewers listen for how you reason: the approach, the trade-offs, the edge cases and the complexity. Practise explaining it, not reciting it.

Sources and review date

Last reviewed 25 October 2026 Statements about other products come from their own public pages: