Number of Islands: which companies ask it and how to practise

Number of Islands is a Medium problem that 81 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 Number of Islands?

Public company lists attribute Number of Islands, a Medium problem, to 81 companies. The most frequent askers are Anduril, Hive and Moloco. 24 reports are from the last six months. It mainly tests array, depth-first search and breadth-first search. Use this as a practice guide, not a promise.

Practise this kind of question aloud

Who asks Number of Islands

81 companies appear in the public lists for this question. By how often each is reported: Anduril (very often), Hive (very often), Moloco (very often), OKX (very often), Rivian (very often), Wix (very often), Zenefits (very often), Snap (very often), TikTok (very often) and Walmart Labs (very often), and 71 more. 24 of them were reported in the last six months, Anduril, Rivian and Snap 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 Number of Islands 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.

Arrays are the default container, so the interviewer is watching how you index, how you avoid a second full pass, and whether you notice when sorting or a hash map would remove a nested loop.

Depth-first search follows one path to its end before backing up. Say how you mark visited nodes and what the recursion depth could be.

Breadth-first search explores level by level, so it finds the shortest path when every step costs the same. Say what goes in the queue and when you mark a node visited.

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/number-of-islands/ (opens the publisher's page). The statement is theirs; we do not reproduce it.

Questions to practise next

If you can solve Number of Islands, try these next, chosen because they share its main topic and many of the same companies: Two Sum (Easy), Merge Intervals (Medium), Best Time to Buy and Sell Stock (Easy), Group Anagrams (Medium), Trapping Rain Water (Hard) and Maximum Subarray (Medium). Each has its own page in the questions list.

Frequently asked questions

Is Number of Islands asked at Amazon?

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

How hard is Number of Islands?

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: