Trapping Rain Water: which companies ask it and how to practise

Trapping Rain Water is a Hard problem that 72 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 Trapping Rain Water?

Public company lists attribute Trapping Rain Water, a Hard problem, to 72 companies. The most frequent askers are Cadence, Goldman Sachs and ThousandEyes. 12 reports are from the last six months. It mainly tests array, two pointers and dynamic programming. Use this as a practice guide, not a promise.

Practise this kind of question aloud

Who asks Trapping Rain Water

72 companies appear in the public lists for this question. By how often each is reported: Cadence (very often), Goldman Sachs (very often), ThousandEyes (very often), Zenefits (very often), X (very often), Walmart Labs (very often), Samsung (very often), Snowflake (very often), Urban Company (very often) and Amazon (very often), and 62 more. 12 of them were reported in the last six months, Goldman Sachs, Snowflake and Amazon 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 Trapping Rain Water tests

It is rated Hard, so a correct brute force with a clear path to the better idea is a good result; interviewers watch how you reason when the answer is not obvious and how you use their hints.

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.

Two pointers walk a sorted or symmetric structure from both ends, or one fast and one slow. The proof that you never skip the answer is what the interviewer is waiting for.

Dynamic programming is solving a problem from the answers to smaller copies of itself. Start with the plain recursion, find the repeated states, then store them; explain what the state means before you write any table.

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/trapping-rain-water/ (opens the publisher's page). The statement is theirs; we do not reproduce it.

Questions to practise next

If you can solve Trapping Rain Water, 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), Number of Islands (Medium), Group Anagrams (Medium) and Maximum Subarray (Medium). Each has its own page in the questions list.

Frequently asked questions

Is Trapping Rain Water asked at Amazon?

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

How hard is Trapping Rain Water?